In a four-year period 115 manic-depressive patients were seen and subsequently followed over a period of 17.8 years. Sixty-five patients had recovered, 24 patients had improved, and 22 had not fully recovered. Several factors may be related to an unfavorable course in manic-depressive illness. More women than men did not recover. Prognosis was somewhat poorer in those patients with mania only, or both manic and depressive attacks of the illness. A history of paranoid delusions seemed to point to a poor prognosis. The prognosis in manic-depressive illness is relatively favorable.