Fibromyalgia syndrome (FMS) is recognizable syndrome characterized by chronic, diffuse pain, an absence of inflammatory or structural muscloskeletal abnormalities, and a range of symptoms that include fatigue, and sleep and mood disturbances. Physical examination and laboratory testing are unrevealing, except for the presence of pain on palpation of characteristic soft-tissue sites, the tender points. Despite the recognition of FMS by the World Health Organization, it remains a controversial condition and its existence as a distinct entity remains uncertain. However, the concept of FMS is a useful one, allowing many investigations to be avoided and appropriate advice on treatment to be given. FMS may overlap with symptoms of, and the patient further impaired by, anxiety and depression. The term FMS dose not imply causation and merely describes the most common symptoms. Many patients with chronic fatigue syndrome(CFS) fulfill the criteria of FMS and represent one end of a spectrum of presentation. Evidence for triggering viral infection and the lower level of serum acylcarnitine, observed in CFS patients, is lacking in the majority of patients with FMS. These findings are suggestive to be distinctively another disorders between FMS and CFS.