The purpose of this investigation was to evaluate the effectiveness of a behavioral treatment package to reduce chronic sleep problems in children with Angelman Syndrome. Participants were five children, 2-11 years-of-age. Parents maintained sleep diaries to record sleep and disruptive nighttime behaviors. Actigraphy was added to provide independent evaluations of sleep-wake activity. The treatment package targeted the sleep environment, the sleep-wake schedule, and parent-child interactions during sleep times. Treatment was introduced sequentially, across families, and evaluated in an interrupted time series, multiple baseline design. Data show that prior to treatment, baseline rates of nighttime disruptive behavior were stable or increasing and none of the participants were falling to sleep independently. With the introduction of treatment, all participants quickly learned to initiate sleep independently. Gradual reductions were reported in disruptive behaviors and these improvements were sustained over time. Results were replicated with two participants when treatment was withdrawn and reinstated. Changes in disruptive bedtime behaviors and in sleep onset were found to be statistically significant. Parents indicated high satisfaction with the treatment. A behavioral treatment package was found to be effective with five children with long histories of significant sleep-related behavior problems. These results suggest that behavioral treatment may be a reasonable way to address sleep problems in some children with Angelman Syndrome.