Right from the very beginning as a medical discipline up to now in psychiatry the paradigms of a disease continuum and of a variety of different disease entities are opposed to each other. The analyses of the historical development of the currently used classification systems indicates that sticking to established terms and methodologies more and more develops to an obstacle in research and treatment. Modern brain research and genetic research require more homogenous clinical syndroms to examine them with scientifically based methodologies and technologies. One first step in this direction could be the widening of Kreapelin's dichotomy of endogenous psychoses with a third spectrum of diseases, the cycloid psychoses, placed between the (bipolar) affective and the schizophrenic spectrum. Cycloid psychoses have a low heritability and are mainly caused by neurodevelopmental disturbances. There are no prodromal negative symptoms before the onset of the disease. There is a liability of developing psychotic symptoms triggered by stress, life events and drugs. There is an acute onset within a few weeks, the course is mostly bipolar with depressive and manic features, remittend and there are no long lasting negative symptoms. Further studies are urgently required in order to confirm or refuse the validity of the concept of the spectrum of cycloid psychoses.