Bipolar disorder and substance use disorder co-occur at very high rates. The high rate is likely due to a complex interaction of biological, social, and psychological factors, and some research suggests that use of substances may be to mitigate symptoms associated with bipolar disorder. Some studies have shown that men with bipolar disorder may be at a higher risk for a substance use disorder than women. The co-occurrence of these disorders leads to poorer treatment outcomes because of higher rates of suicidality, poor treatment adherence, lower quality of life, and more frequent relapse. This population deserves special treatment consideration.