Observations concerning the characteristics of patients who presented
to a medical clinic with a principal complaint of chronic medically un
explained fatigue (Chronic Fatigue Syndrome or CFS) are described, inc
luding the cognitions (thoughts and assumptions) elicited from a sampl
e of these patients who were treated using cognitive behavioural thera
py. On the basis of these observations a cognitive theory of the aetio
logy of CFS is proposed. These observations have implications for the
treatment of patients with CFS.