This paper analyses the relationship between different forms of major mood disorders & suicidal behaviours. Population-based epidemiological surveys as well as clinical studies on the clinically explorable suicide risk factors in bipolar & unipolar depressive disorders are reviewed. The present literature shows that patients with bipolar disorders are at higher risk of attempted & completed suicide than patients with unipolar major depression. Among patients with different clinical manifestations of major mood disorders, bipolar patients in general, & bipolar II subjects in particular, carry the highest risk of suicide. (46 refs.)