Bipolar disorder (BD) affects approximately 2% of U.S. adults and is the most costly mental health condition for commercial insurers nationwide. Rates of BD are elevated among persons with depression, anxiety disorders, and substance use disorders-conditions frequently seen by primary care clinicians. In addition, antidepressants can precipitate manic or hypomanic symptoms or rapid cycling in persons with undiagnosed BD. Thus, screening in these high-risk groups is indicated. Effective treatments exist, and many can be safely and effectively administered by primary care clinicians.