Dysthymic disorder (DD) is defined and distinguished from major depressive disorder (MDD) largely on the basis of its course. Surprisingly, however, there have been few prospective, longitudinal studies of the naturalistic course of DD. This article reports the major findings from a prospective, longitudinal 30-month follow-up study of 86 outpatients with early-onset DD (EOD) and 39 outpatients with episodic MDD. Follow-up assessments included the Longitudinal Interval Follow-Up Evaluation and Hamilton Rating Scale for Depression. Compared with patients with episodic MDD, patients with EOD exhibited less improvement from the baseline evaluation and were more symptomatic at follow-up. Only 39% of patients with EOD recovered from DD during the follow-up period. The diagnosis of DD was fairly stable, with 52% of the EOD group meeting full criteria for DD at follow-up. These data provide prospective confirmation of the chronic course of DD.