Chronic fatigue syndrome, also known as myalgic encephalomyelitis, is an illness of unknown nature and cause, but most medical authorities now accept its existence.1^–3 Research about its cause has been hampered by the absence of a biological marker, the heterogeneous nature of the illness, and difficulties in differentiating cause from effect.2 3 Yet, some progress has been made, particularly when causes are divided into predisposing, triggering, and maintaining factors.

Women get chronic fatigue syndrome more commonly than men for unknown reasons, although increasing evidence suggests a genetic influence on the illness.1 3 Premorbid mood disorders are replicated risk markers for chronic fatigue syndrome;1 3 the risks may be inflated by shared symptoms or they may be markers for those patients with comorbid mood disorders.1 3^–5 Another replicated premorbid risk marker is increased consulting of a doctor for minor illnesses up to 15 years before diagnosis,^{w1 w2} suggesting a general vulnerability for either ill health or seeking health care, the latter possibly being mediated by …