BACKGROUND: Fatigue and psychiatric symptoms are common in the community, but their association and outcome are sparsely studied. METHOD: A total of 1177 patients were recruited from UK primary care on attending their general practitioner. Fatigue and psychiatric disorder was measured at three time points with the 12-item General Health Questionnaire and the 11-item Fatigue Questionnaire. RESULTS: Total scores for fatigue and psychiatric disorder did not differ between the three time points and were closely correlated (r around 0.6). The association between non-co-morbid ('pure') fatigue and developing psychiatric disorder 6 months later was the same as that for being well and subsequent psychiatric disorder. Similarly, having non-co-morbid psychiatric disorder did not predict having fatigue any more than being well 6 months previously. Between 13 and 15% suffered from non-co-morbid fatigue at each time point and 2.5% suffered from fatigue at two time points 6 months apart. Less than 1% of patients suffered from non-co-morbid fatigue at all three time points. CONCLUSIONS: The data are consistent with the existence of 'pure' independent fatigue state. However, this state is unstable and the majority (about three-quarters) of patients become well or a case of psychiatric disorder over 6 months. A persistent, independent fatigue state lasting for 6 months can be identified in the primary-care setting, but it is uncommon of the order of 2.5%. Non-co-morbid (pure) fatigue did not predict subsequent psychiatric disorder.