After Emil Kraepelin's division of psychoses into a group of dementia praecox and manic-depressive insanity, the classification of psychoses with atypical symptoms, which could not be assigned in this dichotomy created a debate, that lasts until our days. These “atypical psychoses” had been described under many terms and concepts in different countries.

In 1926, Kleist coined the term “cycloid psychosis” to describe cases which did not meet the typical presentation shown in Kraepelian's dichotomy. Three decades later, Karl Leonhard established the concept of cycloid psychosis as a nosologically independent group of endogenous psychosis.

Make an historical review of the concept of cycloid psychosis. Discuss the clinical features and debate the classification of this clinical entity.

A bibliographical review is made of the cycloid psychosis, based on the data published in Pubmed.

According to Leonhard, cycloid psychosis generally present with bipolar, polymorphous clinical symptomatology, and run a phasic course with complete remissions after each episode. Furthermore, Leonhard delineated three subtypes: anxiety-happiness psychosis, confusion psychosis and motility psychosis presenting with different symptoms. In 1981, Perris and Brockington formulated the first set of operational criteria for cycloid psychoses. In recent years, new data about this entity have been acknowledged due to information displayed by different clinical studies and imaging techniques.

The phenomenology and classification of cycloid psychosis still needs more evidence for a greater use in clinical practice. However, this clinical entity can solve the void for the diagnosis of many of the so-called “atypical psychoses”.

The authors have not supplied their declaration of competing interest.