ABSTRACT
Owing to the great development in the classification and treatment of mood disorders, in the second-half of the 20th century, clinical studies of this period clearly show that bipolar disorders are much more common than previously believed. The two main sources of this change are the steady and substantial decrease of misdiagnosis of classical manic-depressive (bipolar I) disorder as schizophrenia, as well as the fact that the most recent classification systems such as DSM-IV (1), DSM-IVTR (2), and ICD-10 (3) have made the diagnosis of manic-depressive (bipolar I) disorders more inclusive. The subdivision of bipolar mood disorders further into bipolar I (depression with a history of mania) and bipolar II (depression with a history of hypomania, but not with mania) was proposed almost 30 years ago (4,5). Since then, several studies have demonstrated that bipolar II disorder represents a quite common, clinically and biologically distinct form of major mood disorders that should be separated from both bipolar I and unipolar major depressive disorder (6-11), and that bipolar II disorders show the same-or even worse-psychiatric and social consequences as do bipolar I and unipolar patients (4,12-16).
