Autism has lifetime consequences, with potentially a range of impacts on the health, wellbeing, social integration and quality of life of individuals and families. Many of those impacts are economic. This study estimated the costs of autism spectrum disorders (ASDs) in the UK. Data on prevalence, level of intellectual disability and place of residence were combined with average annual costs of services and support, together with the opportunity costs of lost productivity. The costs of supporting children with ASDs were estimated to be 2.7 billion British Pounds each year. For adults, these costs amount to 25 billion British Pounds each year. The lifetime cost, after discounting, for someone with ASD and intellectual disability is estimated at approximately 1.23 million British Pounds, and for someone with ASD without intellectual disability is approximately 0.80 million British Pounds. (Contains 4 tables.)