AIM It has been reported that rates of epilepsy and mortality are higher among the population with autism spectrum disorder (ASD) than in the general population. The aim of this systematic review is to provide comprehensive evidence for clinicians, carers, and people with ASD regarding these outcomes. METHOD Studies were eligible for inclusion if the main focus of the study involved observation over a period of 12 months or more of an initially defined population (with appropriate diagnostic label). Studies were also required to have at least 30 participants in order to differentiate case series from cohort studies. The Cochrane Database of Systematic Reviews, the Database of Reviews of Effectiveness, MEDLINE, PsycINFO, EMBASE, and CINAHL were searched. The date of the last search was September 2010. The risk of bias of included studies was assessed and ameta-analysis was undertaken. RESULTS Twenty-one studies were identified, 16measuring the percentage of participants with epilepsy and fivemeasuring mortality using a standardized mortality ratio. The pooled estimate for the percentage of participants with epilepsy was 1.8% (95% CI 0.4-9.4%) in studies in which the majority did not have an intellectual disability and the mean age was <12 years at follow-up, and 23.7% (95% CI 17.5-30.5%) in studies in which the majority did have an intellectual disability and themean age at follow-up was more than 12 years. The pooled estimate for the standardized mortality ratio was 2.8 (95% CI 1.8-4.2). INTERPRETATION The prevalence of epilepsy is higher among the population with ASD than in the general population. People with ASD have a higher risk of mortality than the general population. This has important health promotion implications.