The relationship between mood disorders and completed suicide has been investigated in numerous studies during the last few decades. About one-third of all those who have committed suicide have been found to have suffered from major depressive disorder, which is related to about 20-fold suicide mortality as compared to the general population. The prevalence of other unipolar depressive disorders among suicides has been found variable, but also these disorders are associated with markedly increased suicide mortality. Suicide risk among subjects with bipolar disorder is comparable to that of unipolar major depressive disorder, however, there an somewhat conflicting findings concerning the role of bipolar II disorder in suicide. Based on the findings of studies conducted as a part of the National Suicide Prevention Project in Finland, about one-third (31%) of all suicide victims were found to have suffered from DSM-III-R major depression, 27% from other unipolar nonorganic mood disorders (nonmajor depressions), and about 3% from bipolar disorders. For suicide prevention, the findings related to the adequacy of treatment received for depression before suicide seem a major concern. The implications of the findings for suicide prevention include the need for active recognition, treatment and follow-up of depression and suicidal ideation in all health care settings. A crucial question for suicide prevention is the ability of health care to provide effective treatment for depressed male subjects with comorbid mental and physical disorders.