Little is known about the economic impact of autism. This study estimated the economic consequences of autism in the United Kingdom, based on published evidence and on the reanalysis of data holdings at the Centre for the Economics of Mental Health (CEMH). With an assumed prevalence of 5 per 10,000, the annual societal cost for the UK was estimated to exceed ł1 billion. The lifetime cost for a person with autism exceeded ł2.4 million. The main costs were for living support and day activities. Family costs account for only 2.3 percent of the total cost, but a lack of relevant information limited our ability to estimate these costs. Minor improvements in life outcome for people with autism could substantially reduce costs over the lifetime.