The clinical concept of "double depression," i.e., the superimposition of a major depressive disorder in a patient with dysthymic disorder, implies that there are at least some differences between dysthymia, major depression, and double depression. However, the relationship between these two syndromes remains unclear. The present study uses genetic methodology to explore any possible relationship between minor depression, double depression, and major depression. From 1988-1990, all consecutive unrelated inpatients and outpatients (index cases) presenting to a university-based mood disorders service had detailed family histories taken, using modification of the "family history method." Diagnoses for index cases and their first-degree relatives were made according to Research Diagnostic Criteria. For all index cases with a diagnosis of minor or intermittent depression, and minor/intermittent depression plus either single or recurrent depression ("double depression"), morbidity risks for mood disorders were calculated for first-degree relatives (parents, siblings, and children) using the maximum likelihood approach. Results showed no significant differences in morbidity risk calculations to first-degree relatives of index cases with minor/intermittent depression, major depression, or double depression. The data from this genetic perspective suggest that single depression, recurrent depression, minor depression, and double depression are indistinguishable.