Article

When Diagnosis Arrives Decades Late: Understanding the Late Discovery Experience

If you're reading this having recently discovered you might be neurodivergent at 35, or 47, or 63, you're probably cycling through about seventeen emotions simultaneously. Relief. Grief. Anger. Confusion. More anger. A bit of 'am I making this up?' Definitely more anger.

You're not alone, you're not imagining it, and the research is finally starting to catch up with what late-diagnosed people have been saying all along.

A quick note before we dive in: This article focuses primarily on autism and ADHD because that's where most of the research sits at the moment. But giftedness is absolutely part of this late diagnosis conversation too - often intertwined with or mistaken for autism and ADHD. Same goes for OCD, PDA and many others. The experiences overlap significantly, and the lack of recognition causes similar struggles.

The Research Landscape (Or: Buckle Up, I'm About to Throw Numbers at You)

Right, so for starters, the academic world can't quite agree on what "late diagnosis" means. When researchers reviewed 420 studies spanning 35 years, they found cutoff ages ranging from 2 years to 55 years. Only about a third of studies even defined what they meant by "late" (Russell et al., 2025). The most common thresholds? 3 years and 18 years. Which tells you how wildly different the conversation is depending on whether you're talking about a toddler who should have been diagnosed earlier or an adult who's spent decades thinking they were just rubbish at life.

Here's where the UK numbers get properly stark. A 2023 study using English primary care data estimated that approximately 750,000 undiagnosed autistic people aged 20 and above may be living in England (O'Nions et al., 2023). As of 2018, 2.94% of 10-14 year olds had an autism diagnosis compared to just 0.02% of those aged 70 and over. Some estimates suggest only 3.5-7.9% of autistic people aged 50+ have a diagnosis (Stewart et al., 2025).

For ADHD, the picture shows similar patterns. Between 2000 and 2018, only 0.32% of people had an ADHD diagnosis on their health records - approximately one in nine of the likely true number (Renoux et al., 2023). Over 549,000 children and adults were awaiting ADHD assessments in England as of recent figures, with NHS waiting times reaching up to 5 years for adult assessments (Priory, 2025; Renoux et al., 2023).

Between 1998 and 2018, there was a 787% increase in recorded autism diagnoses in the UK (Russell et al., 2022). But this increase wasn't evenly distributed. Women are still diagnosed later, particularly if we don't have obvious language delays. For ADHD, whilst men and women in England self-report similar rates (5.8% vs 5.5%), women experience later recognition and treatment (Martin et al., 2024; NHS England, 2024).

And race matters significantly. In England, Black pupils were 26% more likely to be autistic than white pupils in a 2021 study, yet children who speak a language other than English at home were less likely to have a diagnosis (Roman-Urrestarazu et al., 2021). Research shows children of colour with autism often get labelled with ADHD, conduct disorder, or adjustment disorder first - sometimes after eight or more doctor visits before someone finally recognises autism (Aylward et al., 2021). For ADHD specifically, Asian, Black, and Hispanic children are significantly less likely to be diagnosed compared to white children, even when displaying equal or greater symptoms (Shi et al., 2021; Morgan et al., 2013).

Here's where it gets really interesting: late-diagnosed autism might not just be "missed" early diagnosis. A 2025 study in Nature found only moderate genetic correlation (0.38) between early and late-diagnosed autism, suggesting they might actually be different conditions (Warrier et al., 2025). Researchers at Princeton identified four biologically distinct autism subtypes, including one characterised by reaching developmental milestones on time, having substantial psychiatric challenges, and getting diagnosed later - with genetic disruptions that occur after birth, not just prenatally (Sauerwald et al., 2025).

So when people say "you can't be autistic, you hit all your milestones" - well, turns out there's a whole subtype for that.

The diagnostic criteria themselves carry limitations. The DSM-5 criteria for autism were developed largely based on white males (Haney, 2016). For ADHD, the field trials that established diagnostic criteria included only 21% girls (van der Burg et al., 2024). And until 2013 when DSM-5 came out? You couldn't be diagnosed with both autism and ADHD - clinicians had to choose one, even when both were obviously present.

We're essentially navigating with a map drawn by people who only surveyed one small corner of the territory.

Why Some People Slip Through the Cracks

Let's acknowledge something that might feel contradictory: discovering you're neurodivergent can be simultaneously the most validating and most destabilising thing that's ever happened to you.

For some people, the relief is profound. Finally, an explanation that makes sense. You're not broken or defective or doing life wrong - your brain just works differently. All those struggles weren't character flaws. The exhaustion wasn't weakness. The difficulty with things that seemed easy for everyone else wasn't lack of trying. There's a framework now, a community, a vocabulary for experiences you thought were just... you being difficult.

Others might feel the grief more immediately. For the child who needed support and didn't get it. For the decades spent believing you were fundamentally flawed. For all the coping mechanisms and workarounds you built because nobody realised you needed something different. For the life you might have had if someone had noticed and helped instead of just telling you to try harder.

Some people experience resistance to the realisation. "Oh, so that wasn't my fault? That's a free pass of some sort? Isn't it a bit too easy?" There's often a desire to remain accountable for what you've done and what you're doing. But understanding isn't the same as accepting or justifying - it's simply looking at things from a different perspective so that the course of things can be readjusted, more effectively, more authentically. And for others, there's a different concern: "Oh great, yet another thing to fix." Except it's not to be fixed - it's to be understood, explored, to see how life can be made better as a result.

You might feel angry. At parents who didn't notice, teachers who labelled you lazy, doctors who missed it, a system that failed you. That anger is valid, even if it's not always useful or fair to direct at specific people who were working with the understanding they had at the time - or earlier.

You might feel guilty. Like you're appropriating your child's diagnosis, making their journey about you, being self-indulgent when you should be focused on them. (Spoiler: you're not. This is relevant and valid, and understanding yourself often helps you support them better.)

You might feel imposter syndrome. Like you can't really be autistic or ADHD because you've managed to function this long, hold down a job, have relationships, raise children. Surely if you were "really" neurodivergent, someone would have noticed? (Spoiler again: masking is real, late diagnosis is increasingly common, and functioning doesn't negate neurodivergence.)

You might feel relieved and terrified in equal measure. Relieved to finally understand yourself. Terrified of what this means for your future, your relationships, your sense of identity.

All of these feelings can coexist. They're not contradictory - they're just complex. And complexity is uncomfortable when you're also trying to support your child through their own discovery.

The Misdiagnosis Merry-Go-Round

Before autism or ADHD or giftedness, many of us collect diagnoses like unfortunate souvenirs. Anxiety (tick). Depression (obviously). OCD (why not). Borderline personality disorder (particularly common for women whose emotional responses get pathologised).

Here's what's happening: your coping strategies for navigating social situations get labelled social anxiety. Your executive function struggles get reinterpreted as lack of motivation. Your burnout from years of masking becomes "treatment-resistant depression." Your intense emotional responses to sensory overwhelm get diagnosed as emotional dysregulation disorder.

There's a name for this: diagnostic overshadowing. It's when clinicians see the secondary symptoms - the anxiety, the depression, the overwhelm - and treat those, whilst completely missing the underlying neurodevelopmental difference creating them.

It's like going to the doctor because your shoes don't fit and being prescribed painkillers for your blisters. The blisters might be real, but maybe the actual problem is that you've been wearing the wrong size shoes your entire life.

I've written more about the particular issue of BPD diagnosis in women who are actually autistic in [this academic article exploring whether BPD pathologises women's responses to gendered abuse] - the overlap is significant and the implications are worth examining.

Years of medication that doesn't quite work. Therapy that helps a bit but misses something fundamental. Thinking there's something uniquely wrong with you in a way you can't articulate.

And then finally, someone suggests autism or ADHD, and suddenly everything clicks into a different pattern.

When the Hormones Hit: Perimenopause as Diagnostic Catalyst

Here's something fascinating that happens to many neurodivergent women: we coast along, masked and managing, until perimenopause hits and suddenly all our coping mechanisms stop working.

One woman described it this way: "It was not until I hit menopause - and the hormonal fireworks that come with it - that I finally realised something was different. Not just with how I was responding to the hormonal changes of perimenopause, but with how I was coping with life in general."

It's as if the declining oestrogen strips away whatever buffer allowed masking to work. ADHD symptoms like brain fog and focus difficulties worsen. Sensory sensitivities that had faded roar back. Executive functioning takes what one woman called a "big hit."

Another participant described it as "a perfect storm": "I had so much going on with heading to autistic burnout without even knowing it. I've got multiple chronic health conditions that were manifesting left, right and centre and the perimenopause really kicked those into play."

For some women, this is when everything finally clicks into place. For others, it's terrifying - watching your hard-won coping strategies crumble and not understanding why. Either way, it's common enough that researchers are starting to pay attention to what neurodivergent women have been saying for years: hormones matter.

The Complicated Emotions of Late Diagnosis

Relief and validation tend to be the most common reactions to late diagnosis. Perhaps because by the time you get diagnosed in adulthood, you've spent so long searching for answers that finally having them feels like coming home. Adult-diagnosed individuals often report feeling satisfied, relieved, pleased rather than confused or upset - possibly because the diagnosis explains so much.

But there's also grief. For the child you were - the one who needed help but got labelled "difficult" or "lazy" or "too sensitive." For the teenager who thought they were failing at being normal when actually they were succeeding brilliantly at being themselves in a world not built for their brain. For the young adult who struggled through university or early jobs, convinced they were somehow less capable than everyone else.

And underneath the grief? Often anger. Fury at every teacher who said you weren't trying hard enough. At every GP who dismissed your struggles. At every person who said "everyone feels like that sometimes" when you tried to explain that something felt fundamentally different. At the years - decades - of thinking you were the problem.

The anger often surprises people. You'd think relief would be the dominant emotion, and it often is - but running right alongside it can be this quiet (or not-so-quiet) frustration at all the unnecessary suffering. At the relationships that struggled. At the careers that derailed. At the decades of self-blame for things that were never character flaws to begin with.

Sometimes the anger is hot and immediate: how did they miss this. Sometimes it's cold and slow-burning: I could have had a different life. Both are valid. Both deserve space.

Underneath all of this runs exhaustion. Years of what researchers call "fake it 'till you make it" - performing normalcy, wondering if authenticity would ever be possible. That exhaustion doesn't disappear the moment you get a diagnosis. Sometimes it gets worse before it gets better, as you start to recognise just how much energy you've been expending all along.

The Gap After Diagnosis

One challenge that affects late diagnosis as much as any other is what happens after you finally get that assessment. You might wait years for a diagnosis, finally get one, and then be sent off with a photocopied leaflet.

The assessment focused on proving you're autistic or have ADHD, but nobody seemed to have a clear plan for what comes next. This isn't unique to late diagnosis - it affects children and families too - but it's particularly stark for adults who've spent decades struggling and finally get answers, only to find the support stops at the diagnosis itself.

Understanding your neurodivergence is valuable. Having vocabulary for your experiences matters. Connecting with community can be transformative. But those things often happen despite the system, not because of it.

This is exactly why I focus my practice on post-diagnosis support - that crucial period of "okay, now what?" when you're trying to rebuild your self-concept, develop strategies that actually work for your brain, and figure out how to live authentically after years of masking.

What Actually Matters Now

Whether you were diagnosed at 8 or 48, whether you're formally assessed or self-understanding, whether you're still in that confusing space of "I think I might be..." - what matters is what you do with the understanding once you have it.

Late diagnosis isn't ideal. Earlier support would have helped. Accommodations would have eased struggles. Understanding would have prevented years of self-blame. Let's not pretend otherwise.

But late diagnosis is also a doorway. To self-compassion - understanding that you weren't failing, you were navigating a world not built for your neurology. To community - finding your people who get it without explanation. To authenticity - living as yourself rather than performing normalcy.

The research is catching up, slowly. The healthcare system is learning, glacially. But you don't have to wait for either to give yourself permission to understand your brain, honour your needs, and build a life that actually works for how you are.

If This Resonates

If you're navigating late diagnosis - whether that's processing a recent assessment, sitting with years of self-understanding, or still in that uncertain space of suspecting but not knowing - you don't have to do it alone.

The grief, the relief, the confusion, the clarity, the anger, the peace - all of it deserves space to breathe. Sometimes we need someone who understands that late diagnosis isn't just about getting a label. It's about rewriting your entire life story with new information and figuring out who you are when you're not spending all your energy trying to seem normal.

I work with neurodivergent adults and parents of neurodivergent children, offering neurodiversity-informed, trauma-sensitive counselling. I also support people healing from neurodivergent trauma - the accumulated impact of living unrecognised in systems not built for you.

If that resonates, book a free discovery call through my website at www.equalition.com. We can talk about what late diagnosis means for you, what support might look helpful, and how to move forward in a way that honours both who you've been and who you're discovering you are.

If you're navigating your own late discovery - whether that's processing the grief and relief, understanding what this means for your life now, or figuring out how to advocate for yourself - that's exactly the work I do. Book a free discovery call and let's talk about what might help you through this journey.

Not sure if you want to have a diagnosis? Here's an article that explores that in-between space: Living in Diagnosis Limbo: The In-Between Space

Just got your child's diagnosis and wondering what's next? Start here: We Got the Diagnosis. Now What?