Though a sex difference in the incidence of autism has frequently been reported, few studies have considered sex differences in the severity of features associated with autism. The Autism Diagnostic Interview was used to assess the difference between a group of 21 females and 21 males with autism with equivalent chronological nonverbal IQ greater than 60. Males were rated to be more severely autistic than females on several measures of early social development, but not in any other areas. Results are discussed in relationship to hypotheses based on sex differences in other populations.