From 686 patients attending primary care physicians, 77 were identified by a screening procedure as having chronic fatigue. Of these, 65 were given a comprehensive psychological, social and physical evaluation. Seventeen cases (26%) met criteria for the chronic fatigue syndrome. Forty-seven (72%) received an ICD-9 diagnosis of whom 23 had neurotic depression, with a further 5 meeting criteria for neurasthenia. Forty-nine were 'cases' as defined by the revised Clinical Interview Schedule (CIS-R), and 42 if the fatigue item was excluded. Psychiatric morbidity was more related to levels of social stresses than was severity of fatigue. The main difference between these subjects and those examined in hospital settings is that the former are less liable to attribute their symptoms to wholly physical causes, including viruses, as opposed to social or psychological factors. Identification and management of persistent fatigue in primary care may prevent the secondary disabilities seen in patients with chronic fatigue syndromes.