In the classification of mood disorders, major depressive disorder is separate from bipolar disorders whereas mania is not. Studies on pure mania are therefore rare. Our paper reviews the evidence for distinguishing pure mania (M) and mania with mild depression (Md) from bipolar disorder. Two large epidemiological studies found a prevalence of 1.7-1.8% of M/Md in adolescents and adults. Several clinical follow-up studies demonstrated good stability of the diagnosis after a previous history of three manic episodes. Compared to bipolar disorder, manic disorder is characterised by a weaker family history for depression, an earlier onset, fewer recurrences and better remission, and is less comorbid with anxiety disorders. In addition, mania is strongly associated with a hyperthymic temperament, manifests more psychotic symptoms and is more often treated with antipsychotics. Twin and family studies find mania to be more heritable than depression and show no significant transmission from depression to mania or from mania to depression. Cardiovascular mortality is elevated among patients with mood disorders generally and is highest among those with mania. In non-Western countries, mania and the manic episodes in bipolar disorder are reported to occur more frequently than in Western countries.