DefinitionBipolar disorder involves periods of elevated or irritable mood (mania), alternating with periods of depression. The "mood swings" between mania and depression can be very abrupt.Alternative NamesManic depression; Bipolar affective disorderCauses, incidence, and risk factorsBipolar disorder affects men and women equally. It usually appears between ages 15 - 25. The exact cause is unknown, but it occurs more often in relatives of people with bipolar disorder.Types of bipolar disorder:People with bipolar disorder type I have had at least one fully manic episode with periods of major depression. In the past, bipolar disorder type I was called manic depression.People with bipolar disorder type II have never experienced full-fledged mania. Instead they experience periods of hypomania