Which disorder requires at least one hypomanic episode and one major depressive episode for diagnosis?

Bipolar II Disorder is characterized by the occurrence of at least one hypomanic episode and one major depressive episode. The key aspect of this disorder is the presence of the hypomanic episode, which is a milder form of mania, alongside the more severe major depressive episodes. This combination distinguishes Bipolar II from Bipolar I Disorder, where at least one full manic episode is required for diagnosis.

In Bipolar II Disorder, the hypomanic episodes do not result in significant impairment in social or occupational functioning, nor do they require hospitalization, which is a crucial criterion that contrasts with the manic episodes seen in Bipolar I Disorder.

The other options do not meet the criteria specific to Bipolar II Disorder: Major Depressive Disorder involves only depressive episodes without the hypomanic component, Cyclothymic Disorder consists of numerous periods of hypomanic symptoms and depressive symptoms that do not meet the full criteria for a major depressive episode, and Bipolar I Disorder focuses on manic episodes rather than hypomanic episodes. Therefore, Bipolar II Disorder correctly fits the requirement of having both a hypomanic episode and a major depressive episode for diagnosis.