There is evidence that the risk for recurrence increases with each additional mood episode. Substantial data show that the probability of relapse and recurrence in both unipolar and bipolar disorders can be decreased by extended pharmacologic treatment. In recommending prolonged treatment to prevent recurrence, however, the values of each patient need to be considered, along with the age of onset, the meaning of each mood episode, its severity, and the clinical and social circumstances. Several questions remain to be answered. For instance, are there characteristics of first-episode unipolar or bipolar patients that will indicate whether extended treatment will prevent the next episode? How long should treatment be continued, and at what dose? Given the variety of treatments available for mood disorders, are there particular subsets of patients that are better suited or matched for one agent as opposed to another? What are the characteristics of bipolar patients whose depressive episodes can be treated safely with antidepressants, without risk of switching to mania? What are the costs and benefits of extended treatment, not only in terms of side effects and health service utilization, but also in terms of whether the agents we use may actually worsen the subsequent course of illness? Further questions concern the role of psychotherapy in the continuation and maintenance treatment of recurrent mood disorders. Although few clinicians would advocate psychotherapy alone for treatment of unipolar and bipolar patients at high risk for relapse and recurrence, the specific role of psychotherapy remains to be evaluated. It will be important to determine whether structured psychotherapies can provide additional benefit in terms of both episode prevention and functional outcome. This latter issue is particularly important in view of the substantial social and occupational morbidity even in remitted unipolar and bipolar patients--morbidity which is clearly significant in terms of the overall costs of mental illness. Clearly, more work needs to be done. Even the best studies indicate that a substantial proportion of patients are not helped by current treatments.