Fibromyalgia is a chronic pain syndrome of unknown etiology that is characterized by diffuse musculoskeletal pain, fatigue, sleep disturbance, memory disturbance, and exaggerated tenderness over particular paired locations. Fibromyalgia is found in 2% to 4% of the general population and more common in women, with symptoms usually appearing between 20 and 55 years of age. The diagnostic criteria for fibromyalgia syndrome established in 1990 by the American College of Rheumatology (ACR), includes widespread pain for at least 3 months and point tenderness upon the application of a 4 kg weight at 11 or more of the 18 characteristic tender points. The 2010 ACR preliminary diagnostic criteria have been developed, which are strongly correlated with the 1990 ACR criteria and provide an alternative approach to diagnosis. Patients with fibromyalgia syndrome have lower pain thresholds and experience an altered temporal summation to pain stimuli. The sensitization of pain perception occurs in the dorsal horn of patients with fibromyalgia. However, it is unknown whether sensitization is due to increased pain fiber facilitation, or decreased inhibition. Pregabalin is approved by the United States Food and Drug Administration for the management of fibromyalgia patients. Tricyclic antidepressants, cardiovascular exercise, cognitive behavioral therapy and patient education are also effective in reducing the pain experienced by fibromyalgia patients. This article provides an overview of fibromyalgia syndrome, which is currently thought to be partly responsible for chronic diffuse pain.