The prevalence of autism in Nagoya, Japan: a total population study.

Doctors in Nagoya checked every 18-month-old at city health check-ups for signs of autism. They screened 12,263 toddlers and counted how many met the autism criteria used in 1989.

The team found autism in 0.13% of toddlers, about 1 in every 750 children. That rate was three times higher than the accepted figure at the time.

Akhter et al. (2024) repeated the same kind of count in Bangladesh 35 years later and saw 0.17%, showing the rate has stayed in the same narrow band.

Chiviacowsky et al. (2013) re-checked 1980s Utah files with today’s rules and added 59% more cases. Their work explains why Nagoya’s 0.13% looked high then but would be even higher if we applied current criteria.

Pandey et al. (2008) warn that screens at 18 months miss more cases than screens at 24 months, so Nagoya’s count may still be an under-estimate.

This paper gives you the first solid toddler benchmark: 1 in 750. When parents ask “How common is autism?” you can quote that number and add that today’s tools would find even more. It also tells you 18-month checks are worth doing, but a second look at 24 months will catch kids the first pass missed.