The sleep patterns of two groups of children with autism, one with moderate to severe intellectual handicap, and one with mild handicap to normal IQ level, were compared with those of children without autism. Parents completed 14 day sleep diaries and questionnaires. Results suggested that at some stage during childhood, particularly under 8 years of age, the majority of children with autism will experience sleep problems. These problems are likely to be severe in many cases and will generally include one or more of: extreme sleep latencies; lengthy periods of night waking; shortened night sleep; and early morning waking. Such problems may have some specificity for autism as they appear to be rare in non-handicapped children and in children with mild degrees of intellectual handicap. It is likely that sleep problems in early childhood are related to the severe social difficulties present in autism and the consequent inability of these children to use social cues to synchronise their sleep/wake cycle. Continued sleep difficulties at older ages and with higher IQ may also be related to arousal and anxiety factors.