IntroductionSchizoaffective disorder is a poorly understood disease. In order to better understand it, we have to look at its history. Kraeplin believed that most psychoses could be divided into Dementia praecox and manic-depressive insanity, however this dualistic division was strongly contested and several descriptions of atypical psychoses appeared. In 1933, Kasanin proposed for the first time the term schizoaffective psychosis as a variant of schizophrenia. Since then, and up until 1979, 23 definitions of schizoaffective disorder have been counted. Sometimes different disorders have been called by the same name and similar disorders have different nosological names.ObjectivesTo describe the concepts of schizoaffective disorder, focusing on its historical aspects and the evolution of its diagnostic criteria.AimsTo understand schizoaffective disorder by projecting its nosological position in the future.MethodsWe conducted a literature review using textbooks and PubMed.ResultsSchizoaffective disorder is one of the most confusing and controversial concepts of psychiatric nosological entities.ConclusionsAfter more than 80 years since its first definition, the term schizoaffective remains poorly defined. Indeed, there are studies that do not support the theory that schizoaffective disorder is a separate and distinct mental illness. Thus, the description, characterization, and understanding of this nosological entity continue to be a challenge in the field of mental health.