A hundred and thirty-three affective disorder patients who received prophylactic treatment with lithium were followed prospectively for 5 years and their mortality was recorded. Twenty-two patients died during the period, 13 from natural causes and nine from definite or probable suicide. The observed mortality was significantly greater than the expected overall, and also when natural causes and suicide were considered independently. No patients died from lithium intoxication or lithium-induced side effects. Patients who died from suicide were all bipolars or suffered from affective disorder with uncertain polarity. They were significantly younger than the patients who died from natural causes, they tended to lead isolated lives and they suffered a violent death. The older patients who died from natural causes had often had physical illness and alcohol abuse prior to the start of lithium treatment. The results of the study speak in favour of the establishment of comprehensive treatment programmes possibly in the framework of specialised affective disorder clinics.