It is most relevant to make the differential diagnosis in the several forms of schizophrenia with one another and especially against a number of psychoses. Among the latter ones are Kleist's benign endogenous psychoses, almost always labeled schizophrenias. On the basis of a close criterion at a time pathogenic, pathopsychologic and heredobiologic-evolutional, Kleist describes 25 forms of schizophrenia. These have been ascertained by large and meticulous follow-up, human genetic-minded, after at least 5 years of course. Such set of patterns, initially as well as in the revised form (Tables 1 and 3), is based on the conception of brain systems. It is the specifical working of these systems, within any psychic sphere, that stamps on the clinical variety its distinctive traits. Thus, as shown on Table 2, the schizophrenias may be either systematic or unsystematic in type. The endogenous benign psychoses described by Kleist (Tables 4 and 5) also recognize precise pathogenic dynamisms regarding cerebral systems, which explain the clinical patterns. Their underlying causes are genetic trends, not overt as in the constitutional psychoses, but in latency. This is why Kleist called them degeneration psychoses, atypical endogenous or marginal regards the common ones. Since the term diathesis refers to such latent traits, we assume they may also be called diathetic endogenous psychoses. Some clinical forms follow a cyclic course, other ones occur as isolated attacks. Table 6 shows side by side the diathetic and the schizophrenic forms, according to the spheres and psychic systems envolved. We feel that it is the pathogenic dynamism in both instances what misleads the diagnosis when the psychiatrist does not bear it in mind.