To characterize and quantify the sleep complaints of patients with fibromyalgia (FM) using the Pittsburgh Sleep Quality Index (PSQI).The PSQI was applied to 30 patients with FM according to American College of Rheumatology classification criteria and to 30 healthy controls in individual sessions under similar conditions.The median global PSQI scores were [median (25-75%)] 12.0 (10-16) and 3.0 (2.0-5.0) in patients with FM and controls, respectively (p < 0.001). All PSQI component scores except sleep medications were significantly higher in patients than controls. Sleep latency, sleep disturbances, and daytime dysfunction were the most frequent sleep difficulties experienced by patients with FM.Our results indicate that the PSQI is a useful instrument for characterizing and quantifying sleep disturbances in patients with FM.