Pain, fatigue and a host of other problems are seen in fibromyalgia. CFS displays similar symptoms. However, a practical way to differentiate the disorders is that pain is the predominant problem in people with fibromyalgia, whereas fatigue is the major complaint in people with CFS.

The pain of fibromyalgia is typically chronic and widespread, and is often associated with stiffness. On examination, many patients have specific sites (called tender points) that are extremely tender to touch. The detection of these tender points is helpful in making a diagnosis of fibromyalgia.

The fatigue seen in people with CFS is generally profound, and can be completely incapacitating. Criteria for CFS established by the Centers for Disease Control and Prevention (CDC) are fatigue that has been present for more than six months and is accompanied by the following:

a sore throat;
enlarged or tender lymph nodes;
muscle or joint pain;
other signs of systemic illness.

Signs and symptoms that are commonly present in botfh fibromyalgia and CFS include the following:

sleep disturbances;
headaches;
impaired memory or concentration;
dizziness;
bowel complaints (such as bloating, diarrhea and/or constipation);
anxiety or depression.

[from: http://www.arthritis.org/living-with-arthritis/...]