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Autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) are increasingly diagnosed in Japan, and the rise is no longer limited to children. National data show that adult ADHD diagnoses have overtaken ASD diagnoses, while young adult women have experienced a distinct increase. These trends may reflect greater awareness and changing diagnostic practices, rather than increased prevalence.

A research team was led by associate professor Daimei Sasayama from the Department of Psychiatry at Shinshu University School of Medicine, Japan, along with professor Hideo Honda from the Department of Child and Adolescent Developmental Psychiatry at the same university.

The researchers analyzed Japan's National Database of Health Insurance Claims and Specific Health Checkups, covering approximately 99% of the population, to examine newly recorded diagnoses from fiscal years 2010 to 2023, after a washout period in fiscal year 2009. The study was published in the journal JAMA Network Open on Oct. 20, 2026.

The analysis included 1,621,682 newly diagnosed patients with ASD and 1,483,470 with ADHD. Diagnoses for both conditions were most frequent among children aged 5 to 9 years. However, adult ADHD diagnoses surpassed ASD diagnoses among females in 2013 and males in 2014. Among females, a second ADHD peak emerged at ages 20 to 24 around 2017; by 2020, rates in this group approached the childhood peak.

2% for ADHD. 4% for ADHD. These are projections based on observed diagnosis patterns, not measurements of community prevalence or confirmed lifetime risks; the authors caution that rapidly changing diagnostic trends limit these estimates.

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