Sleep problems are commonly reported in children with autistic disorders. Most studies are based on sleep questionnaires and sleep diaries, but polysomnographic and actigraphic data have also been used. In this study we investigated sleep in older individuals (aged 15-25 years) with autism and Asperger syndrome, using sleep questionnaires, sleep diaries and actigraphy. Although the sleep questionnaires completed by parents and caretakers revealed only a moderate degree of sleep problems, greater sleep disturbance was recorded with actigraphy. Using the latter method, low sleep efficiency (below 85 percent) or long sleep latency (more than 30 minutes) were found in 80 percent of the individuals. There was no early morning awakening, contrary to some earlier reports. This study suggests that even though subjective complaints of sleep disturbances are less common in adolescents and young adults with autism, this may be due to an adaptation process rather than an actual reduction in sleep disturbances.