The essential feature of bipolar disorder (also called manic-depressive illness or manic depression) is a cyclic illness in mood which may shift from deep, frightening depression to extreme excitement, or elation.
The initial episode that leads to hospitalization is usually manic. Both sexes are equally affected.

There does not appear to be a relationship between race and this illness. The age of onset is frequently in late adolescence or the early 20s. For many patients, episodes recur every few years; a few patients have frequent cycles per year.

Some patients have manic or depressive episodes as frequently as 4 times a year and this feature is referred to as rapid cycling.

With increased age, the interval between episode may decrease, and the length of episodes may increase.