Reflex psychosis is a pathogenetic concept of the nineteenth century which has its roots in development of the concept of a reflex arc and its transfer to the understanding of psychiatric diseases. Reflex psychosis stands for different mental disorders caused by a peripheral affection, mostly of the skin, which alters brain function with subsequent psychosis. The concept of reflex psychosis also had an impact in questions of the problem of body and soul. Connections to Descartes' mechanistic theory and humoral pathology are discussed. In addition it influences modern psychiatric models, e.g. the vulnerability-stress concept. When the disease concept was first developed, pro and con arguments occupied neurologists, psychiatrists, pathologists and physicians from other specializations too. In Germany important exponents were Griesinger, Koeppe, Flemming and Schüle. This article deals with the phenomenology, development and fate of this concept.