Aberrant sleep patterns are commonly experienced by girls with the Rett syndrome. In this investigation, the problematic sleep of three girls with the Rett syndrome was regulated using a bedtime fading procedure with response cost. The treatment involved systematically delaying the bedtime and utilized a response cost component, removing the child from bed for one hour, when the child did not experience short latency to sleep onset. Daytime sleep was interrupted, except during regularly scheduled naps. A fading procedure was then successfully utilized to advance the bedtimes. This treatment resulted in more regular sleep patterns for the girls by increasing appropriate nighttime sleep, reducing inappropriate daytime sleep and reducing problematic nighttime behaviors (e.g., night wakings). These preliminary findings are important because they suggest that the dysfunctional sleep patterns of girls with the Rett syndrome may be amenable to behavioral treatments.