Credo Reference-Bipolar DisorderBipolar disorder, also known as manic-depressive disorder, is a type of mood disorder, which occurs in approximately 1% of the population. This rate of occurrence is consistent across groups of diverse ethnicity and culture. In general, bipolar disorder is a long-term illness with an episodic and variable course. Unlike major depressive disorder that is significantly more common in women, the occurrence of bipolar disorder is equally common in men and women. Bipolar disorder is characterized by the presence of mania, or a manic episode, defined as a period of abnormal, persistently elevated, expansive, or irritable mood. An individual need only have one manic episode to fit lifetime diagnostic criteria for bipolar disorder.