The paper deals with a critical appraisal of the state of art of the distinction between bipolar (manic-depressive) and unipolar recurrent affective disorders. However already propounded several years earlier by Leonhard, a distinction between bipolar and unipolar affective disorders has first been taken into general consideration during the last quarter of a century. It is currently firmly established in the most widely accepted international classification systems, and is taken into account in the major psychiatric textbooks. Looking back at the evolution of this distinction, to which research work by the present author has greatly contributed, there are reasons to feel both satisfied and unsatisfied at the same time. Satisfaction arises from the fact that a distinction between bipolar and unipolar affective disorders has contributed to advance our understanding of the nosology of the depressive states, hence, contributing to a higher degree of homogeneity in the populations of patients in research. Dissatisfaction, instead, is born by the ever increasing widening of the scope of the concept of bipolar and unipolar to which current classification systems greatly contribute.