The fibromyalgia syndrome (FMS) is an extraarticular rheumatic disease. Typical features are the chronic, polytopic pain in the musculoskeletal system and the provocation of pain by pressure on defined tender points. Mainly medium age women are affected by the disease. In histomorphological studies of muscle tissue non-specific changes were demonstrated, which were thought to be due to ischemia. Furthermore, sleep disturbance and a reduced pain threshold, which may be related to psychological factors, are discussed in the etiology. In FMS a primary and a secondary form related to other diseases can be differentiated. The treatment consists mainly of behaviour therapy and physiotherapy.