A systematic retrospective case note review was undertaken to investigate autism diagnostic factors in 124 individuals with Sturge-Weber syndrome (SWS). Social Responsiveness Scale questionnaires were then analysed to explore the severity and profile of autism characteristics in 70 participants. Thirty-two to forty percent of participants had a clinical diagnosis of autism and half of those without a diagnosis showed significant social communication difficulties. Children had a relative strength in social awareness and social motivation, which are typically much reduced in people with autism. This finding may explain why, to date, the diagnosis has often been overlooked in this population. The research therefore suggests that children with Sturge-Weber should be screened to identify social communications difficulties and provided with timely support.