Some studies claim to have shown that, compared to the general population, autistic children are born more often in the spring. The current study sought to replicate this finding in a large Dutch sample of mentally retarded autistic patients. Birth data for 1,031 patients with a diagnosis of "Infantile Austism" or "other psychoses with origin specific to childhood" were compared to those of the Dutch national population. Separate analyses were performed on diagnostic subgroups (i.e., infantile autism vs. other psychoses with origin specific to childhood), gender, and intelligence. No evidence was found to suggest that autism is characterized by a deviant birth pattern.