The relationship between severe melancholic and manic states and attenuated or subclinical forms of mood disorders has been recognised since antiquity. The use of the term ‘cyclothymia’ referred to a mood disorder is due to Ewald Hecker, 1877 (Koukopoulos, 2003), a pupil of Ludwig Kahlbaum. His accurate clinical descriptions and his profound knowledge of psychopathology were the forerunners of ... [Show full abstract] modern descriptions of cyclothymia and bipolar disorder (BD) type II. Cyclothymia officially became a part of contemporary nosography with Kraepelin's definition of manic-depressive illness (what we call bipolar disorder nowadays). In addition to traditional forms of mania and melancholy, Kraepelin included within manic-depressive illness some attenuated depressive conditions alternating with episodes of manic excitement of lower intensity (hypomania). He also described long-lasting depressive, manic (hyperthymic), cyclothymic and irritable temperamental traits (which he referred to as ‘basic states’). Thanks to the contribution of Hagop S. Akiskal, the diagnosis of ‘cyclothymic disorder’ was included in DSM-III-TR (APA, 1980) in the chapter ‘Mood disorders’, and subsequently ICD-10 (WHO, 2007) has followed this trend. Cyclothymia received a large empirical validation as a bipolar spectrum disorder, and for this reason it remained classified in DSM-IV-TR (APA, 2000) as an Axis I mood disorder, alongside bipolar I disorder, bipolar II disorder and ‘not otherwise specified’. Specific symptoms were not provided, except for reduced intensity of mood swings and protracted duration (more than 2 years).