The long-term outcome of lithium prophylaxis was explored in 43 bipolar and 36 unipolar patients who had been classified as complete responders after the first 2 years of treatment. These patients were followed up prospectively for a further period of 5 years (treatment period II), during which their psychopathological state was assessed monthly or bimonthly. Forty-nine patients completed treatment period II, 2 died during this period, 7 did not attend the unit any more and could not be traced, and 21 definitively interrupted lithium treatment before the end of the period. In 18 cases the decision to stop lithium was taken by the patient. Twenty-five patients relapsed during the treatment period II. Four relapsers had three or more episodes concentrated during the last 2 years of treatment. These results suggest that the predictive value of an initial favourable response to lithium should not be overrated, and that the impact of the drug on the long-term course of major affective disorders in ordinary clinical conditions might be less dramatic than currently believed.