A double blind, placebo controlled, crossover design study examined overnight sleep physiology, pain, fatigue, and mood symptoms in 12 patients with fibromyalgia treated with cyclobenzaprine. Nine patients completed the study. Patients receiving cyclobenzaprine showed a decrease in evening fatigue (F = 4.7, p less than 0.05) and an increase in total sleep time (F = 4.4, p less than 0.05). Pain, including tender point count and dolorimetry, mood ratings, and alpha non-REM EEG sleep anomaly were unchanged by cyclobenzaprine.