Shinshu University: 1,621,682 new ASD and 1,483,470 ADHD diagnoses in Japan, 2010–2023
Japanese national claims data show adult ADHD diagnoses overtaking ASD, with a second ADHD peak in women aged 20–24. The figures describe diagnoses, not community prevalence.
Researchers at Shinshu University School of Medicine in Japan analyzed newly recorded autism spectrum disorder (ASD) and ADHD diagnoses across the country for fiscal years 2010 to 2023, according to shinshu-u.ac.jp. shinshu-u.ac.jp
shinshu-u.ac.jpshinshu-u.ac.jpOpen source ↗ The team was led by Associate Professor Daimei Sasayama with Professor Hideo Honda. The study was published online on October 20, 2026 in JAMA Network Open (Volume 9, Issue 10).
The source was Japan's National Database of Health Insurance Claims and Specific Health Checkups, which covers about 99% of the population. Fiscal year 2009 served as a washout period.
Diagnosis trends by age and sex
The analysis included 1,621,682 newly diagnosed patients with ASD and 1,483,470 with ADHD. For both conditions, diagnoses were most frequent in children aged 5 to 9 years. Adult ADHD diagnoses surpassed ASD diagnoses among females in 2013 and among males in 2014.
Among females, a second ADHD peak appeared at ages 20 to 24 around 2017. By 2020, rates in this group approached the childhood peak. shinshu-u.ac.jp
shinshu-u.ac.jpshinshu-u.ac.jpOpen source ↗ Of people diagnosed with both conditions, 46.3% received both diagnoses simultaneously. Among those diagnosed at different times, ASD more often came first.
Projected risks and their limits
Based on 2023 diagnosis rates, the researchers projected cumulative risks of receiving a diagnosis by age 49 of 15.7% for ASD and 14.2% for ADHD. For ASD the projected risk was 19.4% in males versus 11.9% in females, and for ADHD 16.9% versus 11.4%.
These are projections from observed diagnosis patterns, not measurements of community prevalence or confirmed lifetime risks. The authors caution that rapidly changing diagnostic trends limit the estimates.
The authors note that the trends may reflect greater awareness and changing diagnostic practices rather than increased prevalence. They suggest that requiring a formal diagnosis to access support may contribute to the high diagnosis rates, but the study did not test this directly. shinshu-u.ac.jp
shinshu-u.ac.jpshinshu-u.ac.jpOpen source ↗
Sasayama said: "We must change society so that everyone is accommodated fairly, whether or not they have a diagnosis." The researchers call for continued monitoring and further investigation of the drivers of these diagnostic patterns.
