Thirty-eight subjects identified in a large community survey were found to attribute their fatigue to 'myalgic encephalomyelitis' (ME). They were matched randomly to two other groups of subjects who attributed their fatigue to either psychological or social factors. All three groups were followed up 18 months later and were asked to complete a series of questionnaires that examined fatigue, psychological distress, number of symptoms, attributional style and levels of disability. At onset the 'ME' group were found to be more fatigued, had been tired for longer but were less psychologically distressed than the other two groups. At follow-up the 'ME' group were more handicapped in relation to home, work, social and private leisure activities, even when controlling for both duration of fatigue and fatigue at time 1, but were less psychologically distressed. The relationships between psychological distress, specific illness attributions, attributional style and their effect on the experience of illness and its prognosis are discussed. Attributing fatigue to social reasons appears to be most protective.