Bipolar disorders are currently divided into 4 entities: bipolar I, bipolar II, cyclothymic disorder, and bipolar disorder not otherwise specified, as described in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). These subtypes of bipolar disorders cover a spectrum of severities, frequencies, and durations of manic and depressive symptoms. The differential diagnosis among these and with regard to other disorders with similar symptom features remains the foundation for treatment of bipolar disorders. It is clear that much diversity exists within these major subtypes, such that designations like "rapid cycling" and "bipolar III" are being put forward and probed for clinical relevance. Some of the concerns and advantages of including these less-established manifestations of bipolar disorders in our diagnostic thinking are discussed here, and the utility and drawbacks of our current diagnostic protocols are considered.