Although most of the care received by bipolar patients occurs during the maintenance phase, relatively little empirical data is available to guide long-term treatment decisions. We review literature pertaining to key questions related to use of pharmacotherapy in the maintenance phase of bipolar disorder. The few double-blind trials with a reasonable sample size are restricted to bipolar I patients and address a modest range of questions mostly related to use of lithium. One rigorous multicenter trial found valproate to have prophylactic benefit. Other studies with valproate alone and in combination suggest efficacy equivalent to lithium and perhaps greater than carbamazepine. Data available for combination treatment are sparse but moderately encouraging. Maintenance treatment with standard antidepressant medications appears destabilizing for some bipolar patients, particularly following a mixed episode. Although some bipolar patients may benefit from combined treatment with a mood stabilizer and a standard antidepressant medication, current knowledge does not allow confident selection of the bipolar patients who might benefit. Clozapine and perhaps other atypical antipsychotics are promising options for maintenance treatment but have not been evaluated in double-blind trials. The numerous other agents used in maintenance treatment are primarily adjuncts to lithium, valproate, or carbamazepine, and information about them is largely anecdotal and uncontrolled. Study design for maintenance trials remains an imperfect art. Conclusions must be drawn cautiously, given the limited generalizability of study designs that accession samples enriched with presumed treatment responders, randomize patients after brief periods of partial remission, abruptly taper prior treatment, make no attempt to distinguish relapse from recurrence, use no formal outcome assessments, or report hospitalization as the only outcome criterion.