Bipolar disorder (or manic depressive illness) is diagnosed when the criteria for major depression has been met but in addition an episode of mania has occurred.

The essential feature of mania is a distinct period when the predominant mood is either elevated, expansive, or irritable, with associated symptoms including hyperactivity, pressure of speech, flight of ideas, inflated self-esteem (grandiosity), decreased need for sleep, distractibility, an excessive involvement in activities that often are flamboyant, bizarre, or disorganized.