Recent meta-analyses on melatonin has raised doubts as to whether melatonin is effective in treating sleep problems in people without intellectual disabilities. This is in contrast to results of several trials on melatonin in treating sleep problems in individuals with intellectual disabilities. To investigate the efficacy of melatonin in treating sleep problems in individuals with intellectual disabilities, we performed a meta-analysis of placebo-controlled randomized trials of melatonin in individuals with intellectual disabilities and sleep problems. Data were selected from articles published on PubMed, Medline, and Embase between January 1990 and July 2008. We examined the influence of melatonin on sleep latency, total sleep time, and number of wakes per night. Quality of trials was assessed using the Downs and Black checklist. Nine studies (including a total of 183 individuals with intellectual disabilities) showed that melatonin treatment decreased sleep latency by a mean of 34 minutes (p<0.001), increased total sleep time by a mean of 50 minutes (p<0.001), and significantly decreased the number of wakes per night (p<0.05). Melatonin decreases sleep latency and number of wakes per night, and increases total sleep time in individuals with intellectual disabilities.