Many of the organic hypotheses arose from the observation that CFS shares a number of symptoms with certain medical conditions. However, it could be argued that there is even greater symptom overlap with primary psychiatric disorder. Debilitating fatigue and sleep disturbances are consistently associated with psychiatric disorder in studies of the community, primary care and tertiary care (David et al. 1990; Pawlikowska et al. 1994). Up to 85 per cent of CFS patients report depression as a key symptom, while between 50 and 70 per cent report anxiety (Komaroff and Buchwald 1991). Further, the current definitions of CFS are based on descriptive phenomenology, the traditional domain of psychiatric, rather than medical, diagnoses.