Outcomes are frequently suboptimal for patients with bipolar disorder who are treated with pharmacotherapy alone. Adjunct exercise has the potential to substantially improve acute and long-term outcomes, although how exercise would improve the course of bipolar disorder needs to be elucidated. We propose that exercise may improve mood and functioning by increasing neurogenesis and reducing allostatic load. We review data suggesting that exercise increases levels of brain-derived neurotrophic factor, which in turn increases neurogenesis and decreases allostatic load. Exercise as a psychosocial adjunct for bipolar disorder should be assessed with rigorous randomized clinical trials.