Smith-Magenis syndrome (SMS) is a clinically recognizable multiple congenital anomaly and mental retardation syndrome caused by an interstitial deletion of chromosome 17 p11.2. Although the physical and molecular genetic features of SMS are increasingly well understood, work is more limited on SMS's behavioral phenotype, which includes self-injury, tantrums, and sleep disturbance. This study examines the sleep behaviors of 39 individuals with SMS, ranging in age from 1.6 to 32 years (mean = 10.5). Prominent sleep problems, seen in 65 to 100% of the sample, included difficulties falling asleep, shortened sleep cycles, frequent and prolonged nocturnal awakenings, excessive daytime sleepiness, daytime napping, snoring, and bed-wetting. Medication to facilitate sleep was used by 59% of SMS subjects. Possible etiologic mechanisms of sleep disturbance in SMS are discussed, as are recommended interventions.