Since its introduction at the end of the nineteenth century, the concept of endogenicity has had a central role in Latin-American psychiatric research and clinical practice. Möbius, a German neuropsychiatrist, in keeping with theories of degeneration, defines as endogenous "all those psychic disturbances that are not a reaction to unfavorable developmental conditions or present stressors nor a direct consequence of bodily alterations". From Möbius on, the concept of endogenicity has been fundamental in the nosological classifications later stated by Kraepelin, Kretchsmer, Schneider, Tellenback and Delgado, among others, thus keeping validity throughout decades. Endogenicity corresponds to one of those psychiatric concepts that trigger strong emotions both in the discussions among specialists and among lay people.