Between 40% and 70% of people with bipolar disorder have a history of substance use disorder. A current or past comorbid substance use disorder may lead to worse outcomes for bipolar disorder, including more symptoms, more suicide attempts, longer episodes, and lower quality of life. Unfortunately, few treatments have been studied in patients with both illnesses, and large controlled trials are needed. Evidence from small studies suggests that some treatments proven for bipolar disorder (e.g., divalproex, lithium, quetiapine, lamotrigine, and psychotherapy) may decrease substance abuse or dependence. Both the bipolar disorder and the substance use disorder should be considered when determining the best management strategy. Once treatment has begun, clinicians should ensure that medication and psychotherapy are administered appropriately and that treatment is modified when there is inadequate response.