Sleep physiology, viral serology and symptoms of 14 patients with chronic fatigue syndrome (CFS) were compared with 12 healthy controls. All patients described unrefreshing sleep and showed a prominent alpha electroencephalographic nonrapid eye movement (7.5-11.0 Hz) sleep anomaly (p less than or equal to 0.001), but had no physiologic daytime sleepiness. There were no group differences in Epstein-Barr virus (EBV) antibody titers. The patient group had more fibrositis tender points (p less than 0.0001), described more somatic complaints (p less than 0.0001), and more depressive symptoms (p less than 0.0001). Patients with CFS do not show evidence for a specific chronic EBV infection, but show altered sleep physiology, numerous tender points, diffuse pain, and depressive symptoms. These features are similar to those found in fibromyalgia syndrome.