This paper describes research on the prevalence, correlates, and treatment of sleep disorders in individuals with developmental disabilities. A significant number of individuals with developmental disabilities have disordered sleep, although prevalence estimates vary from 13% to 86%. Constitutional variables, including age, presence of physical and sensory impairments, and certain genetic syndromes and medical conditions appear to be related to sleep disturbance, but the evidence is mainly correlational and therefore cannot be said to show a causal relation. While a number of behavioral interventions have proven effective in the treatment of sleep disturbance, and drug therapy involving melatonin appears promising, epidemiologic work on the correlates of sleep disorders appear to have had little impact on treatment. Consideration of the nature of sleep disorders may enhance treatments for individuals with developmental disabilities.