The term Chronic Fatigue Syndrome (CFS) refers to a symptom complex of marked and prolonged fatigue for which no identifiable cause can be found. Other symptoms frequently present include generalised muscle weakness and pain, low-grade fever, sore throat, painful lymph nodes in the neck and armpits, exacerbation of fatigue after moderate or strenuous exercise for periods of 24 hours or more, transient pains in a number of joints, and various disturbances of neuropsychological function including confusion, irritability, poor concentration and visual changes. Despite the range of other symptoms being extensive, none are essential for the diagnosis to be made in the presence of profound fatigue of 6 months or more duration. Chronic fatigue syndrome is frequently seen in association with psychiatric illnesses such as depression and anxiety but has not been shown to be causally related to any particular psychiatric disease.