This paper presents the diagnostic criteria for a new subtype of affective disorder, recurrent brief depression (RBD). Data from a prospective longitudinal cohort of young adults from the general population of Zurich, Switzerland, showed that a substantial proportion met all of the criteria for major depression in current diagnostic systems except duration. The validity of the subtype of RBD was examined according to clinical manifestations, severity, longitudinal course, and family history. RBD was found to be similar to major depressive disorder (MDD) on most of the indicators of validity including symptomatology, association with somatic and psychiatric disorders, age at onset, family history, longitudinal course and levels of impairment, except duration of depressive episodes. This suggests that RBD constitutes a valid subtype of affective disorder. The major implications of these findings are that both recurrence and duration should be considered in developing diagnostic thresholds for depression and in assessing the severity of affective disorders.