AbstractReviewing the development of concepts of ‘atypical’ psychoses in European countries and in the United States shows that there are various terminologies which are given to a group of psychoses unclassifiable within Kraepelinian dichotomy. Bouffee delirante (French school), cycloid psychoses (Leonhard, Perris), reactive psychoses (Scandinavian school) and acute schizoaffective psychoses (Kasanin) are the most common terms. These are consistent in terms of acute onset, polymorphic symptomatology and good prognosis, and are considered to be distinct from major psychoses, especially from typical schizophrenia. The concept atypical psychoses in Japan was developed under the influence of Mitsuda's clinico‐genetic studies. According to Mitsuda, atypical psychoses are not mere phenotypical variants of typical schizophrenia and manic‐depressive psychosis (MDP) but belong to a genetically different category and are probably heterogeneous. The characteristic features in the Japanese concept of atypical psychoses emphasizes the alteration of consciousness in symptomatology and pays attention to the nosological relationship with epilepsy, as well as with schizophrenia and MDP. Thus, in Japan it is generally considered that atypical psychoses are independent of ‘typical’ major psychoses and are located nosologically in the border area between typical schizophrenia, MDP a