Recent studies have indicated that bipolar disorder is more common than previously believed. The socioeconomic and personal burdens of this illness are significant, and the lifetime risk of suicide attempts by patients with bipolar II disorder is high. It is not uncommon for patients with bipolar disorder, especially those presenting with depression, to be seen first in a primary care setting; therefore, primary care physicians need to be ready to diagnose and manage patients with these mental illnesses. The diagnosis of bipolar disorder or bipolar spectrum disorder is easily missed, or these illnesses may be misdiagnosed. A systematic and detailed initial history from the patient and a reliable family member is essential to making the correct diagnosis. The Mood Disorder Questionnaire, a validated screening instrument for bipolar disorder, may help primary care physicians make an appropriate diagnosis. Long-term management of patients with bipolar disorder should involve close liaison with a psychiatrist.