This article reviews the concept, nosological status, diagnostic features, associated clinical characteristics, and the etiopathological variables involved in cycloid psychosis. The concept of cycloid psychosis is based on sound psychopathological and course underpinnings, and despite the inclusion of some cycloid features in the current diagnostic systems such as ICD-10 and DSM-IV, these systems do not capture well the diagnostic construct of this disorder. Cycloid psychosis is a valid clinical constructs that can be easily differentiated from the boundary disorders on clinical grounds. It seems to be heterogeneous from the etiopathological point of view, in that a variety of factors seems to be involved to a different degree in most of the patients. Future studies should examine putative subtypes of the disorder in relation to etiological, pathophysiological and clinical variables.