The authors studied the risk of relapse among depressed patients after cognitive behavior therapy in order to document the need and potential indications for longer-term models of treatment. Forty-eight patients with major depression who responded during a 16-week course of cognitive behavior therapy entered a 1-year prospective follow-up study, as did two patients who received 20 weeks of therapy. Standardized, independent clinical assessments were completed 1, 3, 6, 9, and 12 months after treatment. Relapse was defined as, at minimum, a 2-week period in which the subject met the DSM-III-R criteria for major depression and had a Hamilton depression scale score of 15 or more. Sixteen patients (32%) relapsed during the 1-year follow-up. Correlates of relapse included a history of depressive episodes, higher levels of depressive symptoms and dysfunctional attitudes, slower response to therapy, and being unmarried. Patients who fully recovered during therapy (Hamilton depression score of 6 or less for 8 weeks or more) were at significantly lower risk for relapse than those who partially recovered (9% and 52%, respectively). Slower response to therapy, unmarried status, and high residual scores on the Dysfunctional Attitudes Scale were independently and additively related to increased risk of relapse. These findings provide further evidence of a relation between residual symptoms and relapse after cessation of active treatment. The authors strongly recommend that models of longer-term psychotherapy be developed for depressed patients who do not recover fully during time-limited cognitive behavior therapy.