J Rheumatol
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To examine the independent effects of chronic regional and widespread pain syndromes on health and functional status after accounting for comorbid chronic fatigue using a co-twin control design. ⋯ Both chronic regional and widespread pain exact debilitating effects on perceived general health, physical functioning, and sleep quality independent of CFS. However, the psychological and psychiatric influence of chronic pain appears closely tied to CFS. Research should examine the additive role of CFS-like illnesses in patients with chronic pain, and its influence on treatment and outcome.