Objective: Variations in month of birth were examined in patients with infantile autism to test the hypothesis that birth in a particular month may be a risk factor for this disorder. Method: Data for autistic patients registered with the National League for Autism in Israel (N=188) during the years 1964-1986 were compared with data on monthly distribution of live births in Israel for the corresponding period. Results: After risk ratio estimates were computed for children born with infantile autism for each month, a significant increase was observed for children born in March and August. This association was true for each year throughout the study. An additional finding was a significantly higher rate of birth of autistic children in the years 1970-1976. Conclusions: This study, although made in a different climatic area than three earlier studies, further emphasizes the earlier findings that March and August births are a risk factor for development of autistic disorder.