Marital adjustment and treatment outcome were evaluated in the Treatment of Depression Collaborative Research Program, a multicenter clinical trial evaluating interpersonal psychotherapy, cognitive therapy, imipramine, and placebo. Marital adjustment and depression were assessed pre- and posttreatment, and depression was assessed at 6, 12, and 18 months after treatment. Results indicate that (a) there was a significant improvement in marital adjustment after treatment, (b) this effect was not moderated by treatment type, and (c) this effect was mediated by change in depression. Poor pretreatment marital adjustment was modestly associated with negative outcome, whereas poor posttreatment marital adjustment was strongly associated with negative outcome during follow-up. The findings suggest that poor marital adjustment at the end of active treatment is a risk factor for increases in depression severity during follow-up.