This paper examines doctors' and patients' views on the consequences of an increasingly common symptomatic diagnosis, chronic fatigue syndrome (CFS). Two studies were conducted: the first comprised interviews with 20 general practitioners; the second was a longitudinal study, comprising three interviews over a period of 2 years with 50 people diagnosed with CFS. Contrasts were apparent between doctors' practical and ethical concerns about articulating a diagnosis of CFS and patients' experiences with and without such a diagnosis. Seventy per cent of the doctors were reluctant to articulate a diagnosis of CFS. They felt constrained by the scientific uncertainty regarding its aetiology and by a concern that diagnosis might become a disabling self-fulfilling prophecy. Patients, by contrast, highlighted the enabling aspects of a singular coherent diagnosis and emphasized the negative effects of having no explanation for their problems.