There has been widespread debate about the validity of the contemporary diagnostic classification system of depression. The major goal of this study is to examine the prognostic significance of each of the major subtypes of depression using data from 5 interviews of a 15-year prospective community-based cohort study. The stability of the following diagnostic subtypes across the duration of the study was examined: major depressive disorder (MDD), dysthymia, recurrent brief depression (RBD), and minor depression. The results show that there was little stability for the specific subtypes of depression among those who continued to manifest depression during the follow-up period; 51% of those with MDD and 44% of those with RBD met criteria for another subtype of depression. When stability was observed, the same subtype often occurred in combination with the development of another subtype. Among individuals with a single subtype, severity was greatest among those with dysthymia, whereas individuals with combined subtypes had greater severity than those with a single subtype. The lack of longitudinal stability of the diagnostic subtypes of depression suggests that depression is better expressed as a spectrum rather than a set of discrete subtypes.