The following is also from The Fibromyalgia Network:

"Long term follow-up studies on fibromyalgia syndrome have shown that it is chronic, but the symptoms may wax and wane. The impact that FMS can have on daily-living activities, including the ability to work a full-time job, differs among patients. Overall, studies have shown that fibromyalgia can be equally as disabling as rheumatoid arthritis. On the other hand, follow-up of people meeting the chronic fatigue syndrome criteria indicates that as many as 40% may significantly improve but few are thought to completely recover from this syndrome. Longer term follow-up studies are not available to indicate whether these "improved" CFS patients later relapse with an increase in symptoms. A preliminary follow-up study by the CDC (Centers for Disease Control) reveals that for those individuals with chronic fatigue syndrome who do not recover or significantly improve after five years duration, their most prominent symptom changes from fatigue to muscle pain with concentration problems (sounds a lot like the permanent syndrome of fibromyalgia but the CDC is not checking patients for tender points). According to a research study by Dedra Buchwald, M.D., people who meet the criteria for both FMS and CFS tend to be at the more severe end of the spectrum of symptoms and are more likely to become work-disabled. Buchwald says her findings underscore the importance of recognizing concurrent fibromyalgia and chronic fatigue syndrome (Rheumatic Disease Clinics of North America 22(2):219-243, 1996)."