A high proportion of children with epilepsy have autism spectrum disorder. Although estimates vary, depending both on the population studied and the definitions used, a figure of around 20% has typically been reported. Autism can have a major impact on the life of the child and family. Despite the importance of this comorbidity and although many studies have been performed, a full understanding of the possible links between epilepsy and autism remains elusive. In a minority of cases, for example in the Landau-Kleffner syndrome, the autistic features can be the result of the epilepsy itself. However, there has been a failure to demonstrate that the epilepsy itself plays a major role in most cases. The current evidence seems to point to a common underlying predisposing factor. The discovery of a growing number of genetic defects leading to both conditions would support this explanation of the link.