Sleep and fatigue characteristics were evaluated in 72 patients who met major criteria for the chronic fatigue syndrome (CFS), 57 multiple sclerosis (MS) patients preselected for fatigue complaints, and 40 healthy controls. Using previously validated rating scales, CFS patients had significant elevations in fatigue and sleep disturbance compared to the MS and healthy control groups. To confirm these subjective measures, polysomnography was carried out in a subgroup of CFS patients who included sleep disturbance as one of their symptoms on initial clinical interview. In 10 of 16 (62.5%) polysomnography revealed clinically significant and potentially treatable sleep abnormalities. Their sleep disorders included periodic movement disorder (4), excessive daytime sleepiness (3), apnea (2), and narcolepsy (1). We conclude that subjective sleep disturbance is common in CFS and some CFS patients may have objective sleep disorders.