Background. Outcome studies of chronic fatigue, neurasthenia and other unexplained fatigue syndromes are few and have been carried out in developed Western countries. This paper aimed to study the outcome of unexplained fatigue syndromes in an international primary care sample and to identify risk factors for persistence.

Method. We used data from the WHO collaborative study of psychological problems in general health care, in which 3201 primary care attenders from 14 countries were followed-up for 12 months. The assessment included a modified version of the Composite International Diagnostic Interview.

Results. Unexplained fatigue persisted in one-fifth to one-third of the subjects depending on the definition of fatigue. From the factors studied only severity of fatigue and psychiatric morbidity at baseline were associated with persistence 12 months later. Outcome did not differ between countries of different stages of economic development.

Conclusions. The prognosis of fatigue syndromes in international primary care is relatively good. The study underlines the importance of psychological factors in influencing short-term prognosis.