OBJECTIVE: To quantify the effect on adherence likelihood of patients' preferences for short-term outcomes and side effects of bipolar disorder treatments. METHODS: Patients with bipolar disorder (n=469) completed a choice-format conjoint or stated-preference, web-enabled questionnaire that included a series of 11 hypothetical treatment choices. Each treatment alternative specified and varied the frequency and severity of manic episodes and the frequency and severity of depressed episodes, in addition to weight gain, cognitive difficulties, fatigue, and the risk of developing a life-threatening side effect. The patient's current treatment was included as one of 3 alternatives in 6 of the choice tasks. Each choice task was followed by a question on likely adherence to the chosen treatment. RESULTS: Patients preferred milder episodes of mania and depression. Reduced frequency of manic and depressive episodes contributes significantly to patients' satisfaction with treatments. The likelihood of choosing a treatment with an interval between mania episodes of 4-6 months is 2.5 times greater than the likelihood of choosing a treatment with an interval between manic episodes of 2-3 months. Patients were willing to sacrifice symptom control to avoid significant weight gain or cognitive effects. For example, the reduction in patient satisfaction from a 10-20 lb gain in weight compared to a 2-10 lb weight gain was similar to the difference in patient satisfaction between a severe and mild manic episode. Fatigue and risk of a life-threatening side effect were the least important attributes. Factors that reduce likely adherence are rapid cycling, significant weight-gain experience, and severe fatigue or cognition problems. CONCLUSION: In this study bipolar patients were willing to sacrifice mood-control benefits of therapy to avoid side effects, particularly weight gain and cognitive side effects. Preferred treatments encourage quantitatively significant improvements in stated adherence and thus should improve long-term treatment outcomes.