Can timely diagnosis and treatment of depression reduce the risk of suicide? Studies of treatment effects on mortality in major mood disorders remain rare and are widely considered difficult to carry out ethically. Despite close associations of suicide with major affective disorders and related comorbidity, the available evidence provides little support for sustained reductions of suicide risk by most mood-altering treatments, including antidepressants. Studies designed to evaluate clinical benefits of mood-stabilizing treatments in bipolar disorders, however, provide comparisons of suicidal rates with and without treatment or under different treatment conditions. This emerging body of research provides consistent evidence of reduced rates of suicides and attempts during long-term treatment with lithium. This effect may not generalize to proposed alternatives, particularly carbamazepine. Our recent international collaborative studies found compelling evidence for prolonged reduction of suicidal risks during treatment with lithium, as well as sharp increases soon after its discontinuation, all in close association with depressive recurrences. Depression was markedly reduced, and suicide attempts were less frequent, when lithium was discontinued gradually. These findings indicate that studies of the effects of long-term treatment on suicide risk are feasible and that more timely diagnosis and treatment for all forms of major depression, but particularly for bipolar depression, should further reduce suicide risk.