How long does an autism or ADHD assessment take?

When people ask whether an adult assessment is worth pursuing, the honest answer includes “how long it takes”, and most figures floating around are anecdotes. This is one of the few studies that measured waits from real clinical records across most of a country’s public system, for adults as well as children, and for ADHD as well as autism.

It’s also a useful kind of paper for this section because its numbers are precise and its scope is narrow. Knowing exactly what they cover is most of the job.

Diagnosis matters to people: for understanding, for support, and for explaining why earlier help didn’t work. The waits are known to be long, but the reasons are hard to pin down, because studies tend to use either administrative data with no clinical detail or small research samples. The team asked three things: how long do children and adults wait, do demographic and clinical factors change the wait, and does following best-practice standards slow things down or speed them up.

Donald Maciver and colleagues at the National Autism Implementation Team, a Scottish Government-funded group that includes neurodivergent members, asked all fourteen of Scotland’s health boards to take part. Ten agreed; four declined, citing workload. Thirty diagnosing teams, 18 for children and 12 for adults, each pulled their most recently completed cases, working backwards until they hit a quota. That produced 408 cases: 206 children and adolescents, average age nine at referral, and 202 adults, average age thirty.

Local staff extracted the data from case notes: dates of every step, demographics, medical and developmental history, number of appointments, and whether the team had followed each of thirteen best-practice standards. The wait was measured from referral to the written diagnosis, in three stages: time to first appointment, length of assessment, and time to communicate the result. The team then modelled which factors were associated with longer or shorter total waits.

The waits. Median total wait was 252 days for adults and 525 days for children, and the spread was wide: a quarter of adults waited more than 611 days, a quarter of children more than 857. The first appointment was the long part for adults, a median of 106 days; once underway, adult assessments took a median of 56 days. Children waited a similar 106 days to start but then a median of 214 days in assessment. Against Scotland’s proposed 252-day target for the whole process, 47 percent of adults and 20 percent of children made it.

Who waited longer. Among adults, an ADHD diagnosis meant a longer wait than an autism diagnosis, about 63 weeks against 39, which the authors put down to autism pathways being more established. Adults with more complex histories, such as intellectual disability or a family history of neurodevelopmental conditions, were seen faster, probably because they were triaged as more likely. Children with complex histories waited longer, probably because more people and settings had to be involved. Being female, from a minority-ethnic background, or speaking a language other than English at home made no measurable difference.

Who got assessed at all. Most people who completed an assessment got a diagnosis: 83 percent of children and 88 percent of adults. Getting more than one was uncommon. Children’s services saw almost two boys for every girl, most starkly under age ten; adult services were evenly split. Fetal alcohol spectrum disorder, thought to be at least as common as autism, was diagnosed once in 408 cases.

Did doing it properly slow it down? No. For children, following more of the best-practice standards went with shorter waits, especially good information gathered before referral. For adults the picture was unclear, partly because the standards were written for children. More appointments went with shorter adult waits.

Not how long you will wait. These are medians from one country’s public system in one eight-month window. They can’t be read across to England, the US, private assessment, or today.

Not the full picture, and probably not the worst of it. Four health boards declined, citing workload, and the authors say the most strained teams, likely with the longest waits, may have opted out. Some services turn referrals away rather than waitlist them, and those people appear nowhere in this data. The figures are, if anything, optimistic.

Not a fair comparison between adults and children. Adult services in the UK often accept only people with moderate to severe mental illness, so they see a narrower, more urgent group. The authors warn that the adult system’s apparent efficiency should be read with that in mind.

Not much about ethnicity. About 4 percent of cases were from minority-ethnic backgrounds, which matches Scotland’s population but is too few to test. “No difference found” here means “couldn’t be tested”, not “no difference”.

Not a normal year. The cases were completed in 2021 and 2022, when pandemic backlogs and a surge in people recognising neurodivergence in themselves collided. Some children’s services had stopped assessing entirely during lockdowns.

The value of this paper is that it measured a thing everyone talks about and nobody had numbers for, and it measured it from the records rather than from memory. The 252 and 525 day medians are the most solid figures available for a public system, and the authors are unusually clear that they’re a floor.

Two findings deserve more attention than the headline. Adults with ADHD waited longest, because the pathways for ADHD are younger and thinner than for autism, which matches what adults with ADHD report everywhere. And children’s services saw two boys for every girl while adult services were balanced, which is the diagnostic gap showing up in the queue itself.

The authors’ own conclusions are worth carrying. Service factors mattered at least as much as individual ones, and service factors can be changed. They argue against limiting diagnosis to people in crisis, call it ethically wrong, and float pathways that start from self-identification with full assessment available when needed. That’s a clinical team, funded by a government, saying the gate is in the wrong place. We agree.

It represents people who completed a public-sector neurodevelopmental assessment in Scotland in 2021 and 2022: mostly White Scottish, mostly autism or ADHD, adults mostly in their twenties and thirties. It doesn’t represent people who were refused a referral, people assessed privately, people outside Scotland, or the teams too overloaded to take part.

The same measurement repeated after the pandemic surge, and in other UK nations. Data on the people who are turned away before a waiting list, who are invisible here. Adult-specific quality standards, which the authors say are missing. And an evaluation of the transdiagnostic and self-identification pathways the paper recommends, so the argument for moving the gate has evidence behind it.