Background Disturbances in circadian rhythm functioning, as manifest in abnormal sleep–wake cycles, have been postulated to be present in people with autistic spectrum disorders (ASDs). To date, research into the sleep–wake cycle in people with ASDs has been primarily dependant on third-party data collection. Method The utilization of non-invasive objective recording technologies such as actigraphy permits investigation of both sleep and circadian rhythm functioning in people with ASDs, together with the collection of data on daytime activity. Results Data were collected from 31 participants with intellectual disabilities living in supported community-based residential provision aged between 20 and 58 years, of whom 14 had an ASD. Analysis indicated that there were no significant differences in sleep patterns and circadian rhythm function between those participants with an ASD and those without. Conclusions The mean scores of the participants as a whole indicated abnormalities in the two key circadian rhythm parameters of interdaily stability and intradaily variability. The implications of these findings for both clinical practice and theory are discussed.