The authors report prospective uniform clinical data differentiating 25 patients who committed suicide from 929 patients who did not in a group of 954 patients with major affective disorder followed for an average of 4 years in the Collaborative Program on the Psychobiology of Depression. Eight (32%) of the suicides occurred within 6 months and 13 (52%) within 1 year of entry into the study. Hopelessness, loss of pleasure or interest, and mood cycling during the index episode differentiated the suicide group. Diagnostic subcategories, suicidal ideation at entry to the study, suicide attempts during current or past episodes, and medical severity of prior attempts did not differentiate the suicide group.