The lifetime prevalence of bipolar I disorder is approximately 1%. However, the prevalence of bipolar spectrum disorder is substantially higher. Bipolar spectrum disorder is a longitudinal diagnosis characterized by abnormal mood swings comprising some of the following cross-sectional clinical states: mania, hypomania, mixed states, hyperthymic temperament, major depressive episode, and depressive mixed state. Most bipolar spectrum patients present for treatment during a depressive episode, and therefore clinicians often miss the diagnosis of bipolar spectrum disorder. Several studies have documented that patients often wait as long as 10 years for the correct diagnosis of bipolar spectrum disorder. One way to increase recognition of bipolar spectrum disorder is to screen for it. A recently introduced screening instrument for bipolar spectrum disorder, the Mood Disorder Questionnaire, is described.