The prevalence of autism spectrum disorders for children with epilepsy in the general population is unknown. In a prospective community-based study of newly diagnosed childhood epilepsy, autism spectrum disorder was determined from parental interviews, medical records, and expert reviews by a child psychiatrist. A total of 28 (5%) participants had autism spectrum disorders. West syndrome (prevalence ratio = 4.53, P = .002) and intellectual impairment (prevalence ratio = 4.34, P = .002) were independently associated with autism spectrum disorder. Absent West syndrome, male gender was associated with autism spectrum disorder (prevalence ratio = 3.71, P = .02). For participants with overall normal cognitive abilities, 2.2% had autism spectrum disorder, which is substantially higher than estimates from the general population (0.5%-0.9%). In addition to West syndrome, which has repeatedly been shown to have a special relationship with autism spectrum disorder, the most important determinants of autism spectrum disorder in the general population (intellectual impairment and male sex) are also important in young people with epilepsy.