The prevalence rate of autism has been reported as 0.04% to 0.05%, but one recent study in Japan found prevalence of 0.16%. The authors have been involved in routine well-child medical examinations at 18 months of age, at the Midori Public Health Center in Nagoya. A statistical survey of diagnoses was made from April 1979 to March 1984 for the purpose of conducting an epidemiological study of autism. Of 12,263 children examined, 168 were identified as having developmental problems and, of these, 139 underwent a second examination. Autism was diagnosed in 16 of these children and a category called "autism suspected" was defined in an additional 10 of these 139 children. The 16 cases of autism gave a minimum prevalence of 0.13%, three times the usually reported rate. The validity of the higher prevalence rates is discussed.