Fibromyalgia: A disease characterized by chronic pain, stiffness, and tenderness of muscles, tendons, and joints, without detectable inflammation. Fibromyalgia does not cause body damage or deformity. However, undue fatigue plagues 90 percent of patients with fibromyalgia. Sleep disorder is also common in patients with fibromyalgia. Fibromyalgia can be associated with other rheumatic conditions, and irritable bowel syndrome (IBS) can occur with fibromyalgia. There is no definitive medical test for the diagnosis of fibromyalgia, so diagnosis is made by eliminating other possible causes of the symptoms. The most effective treatment is a combination of education, stress reduction, exercise, and medication. Formerly known as fibrositis.