Although the traditional nosological view interprets mania as strictly connected with depression in the context of manic-depressive illness, unipolar mania (UM), that is, the lifetime occurrence of mania or hypomania in the absence of depression, has been proposed as a necessary diagnostic entity. Epidemiological data estimate that at least 5% of people with type I bipolar disorder never experienced depression. These subjects are more often males with a hyperthymic temperament, a younger age at onset, and more psychotic features. Current classification systems do not formally recognize UM, but different definitions of mania without depression have been proposed. UM should be assessed according to the number of mood episodes, the predominance of manic or hypomanic episodes, and its clinical course. More generally, UM should be considered in the context of an affective spectrum including different clinical phenotypes based on the predominance of depressive or manic symptoms. Additional clinical and epidemiological research in this field is needed.