The sleep patterns of a cohort of 83 Rett syndrome females were characterized using a sleep diary for 7 consecutive days and nights and compared with normative sleep data. The mean total sleep time of the cohort was 10.75 h, daytime sleep 0.77 h, sleep efficiency 89.7%, and sleep latency 0.52 h. When subjects were categorized according to age and Rett syndrome classification, there was no significant difference in their sleep characteristics. There was a significant difference in the percentage predicted total sleep time (P<0.001) and Z scores for total sleep time (P<0.001), when subjects were categorized according to age and compared with normal children. The Rett syndrome subjects in this study did not show the age related decrease in total and daytime sleep time seen in normal children. The immature sleep pattern demonstrated in this cohort, may be a consequence of arrested brain development.