Chronic fatigue syndrome (CFS) is a chronic illness of uncertain aetiology characterized by at least six months of debilitating fatigue and associated symptoms. The symptoms of the syndrome are all non-specific and some (but not all) are also seen in psychiatric illness. The symptomatology suggesting an organic component to the illness includes its abrupt onset with an 'infectious-like' illness, intermittent unexplained fevers, arthralgias and 'gelling' (stiffness), sore throats, cough, photophobia, night sweats, and post-exertional malaise with systemic symptoms. The illness can last for years and is associated with marked impairment of functional health status.