Despite the high prevalence of unipolar depression in the general population, few genetic studies are available on subtypes of unipolar illness. We evaluated morbid risks for depression, alcoholism and/or sociopathy in the relatives of early onset (before age 40) and late onset (after age 40) unipolar patients in a sample of 106 probands consecutively admitted to the New York State Psychiatric Institute. unipolar patients with an early onset disease have a greater familial morbidity for depression, alcoholism and sociopathy than unipolar patients with a late onset disease. There is an excess of unipolar depression in female relatives of early onset unipolars when compared to late onset probands, regardless of the proband's sex. Alcoholism and sociopathy are also more prevalent in the relatives of early onset unipolars versus late onset probands. Our morbidity risk data show familial genetic differences between early and late onset forms of unipolar illness and partially confirm Winokur's concept of two subtypes of unipolar depression.