A diagnostic questionnaire was used to study the abnormalities that parents first noticed, the ages at which parents first noticed these early symptoms, and the main problems the parents complained about in the first consultation. In this study, parents of 141 autistic children below the age of 12 were employed. Approximately 71% of the parents noticed abnormalities in their autistic children by the age of 2 1/2 years. Parents of older autistic children tended more often to report symptoms of mental retardation, ritualistic behavior, and self-injury. This study showed that the Japanese peak of abnormal social behavior, including autistic symptoms as reported by parents, was from the ages of 3 years to approximately 9 years, compared with the U.S. and European peak of 3 to 6 years.