A.Fibromyalgia (FM) and chronic fatigue syndrome (CFS) have many similarities. In fact, a number of people with FM also have CFS, which can make diagnosis and treatment even more confusing. Although the two illnesses have many symptoms in common, the most prevalent symptom of FM is widespread pain while the primary symptom of CFS is extreme fatigue that does not improve with rest. The differences in the diagnostic criteria reflect this emphasis on the primary symptom. Fibromyalgias diagnosis revolves around the pain, while chronic fatigue syndromes diagnosis focuses more on the fatigue.