On the basis of the results provided by clinical follow-up, clinico-epidemiological and clinico-genealogical studies, the authors have reviewed the systematics of the major forms of schizophrenia developed at the Institute of Psychiatry of the USSR Academy of Medical Sciences and offer a statistical characteristics of these forms. The authors specifically discussed the questions associated with the characteristics of the syndrome formation and course of slowly progressive (torpid) schizophrenia and the place these forms occupy in the modern foreign classifications, including the DCM-III). The paroxysm-like form was established to run predominantly the course with a small rate of attacks or the "one-paroxysm" course. Slowly progressive and psychotic forms of continuous schizophrenia were shown to be relatively continuous, being characterized by not only the signs of tortuosity of the course but also by those of regression and subsidence of the process. Attention is drawn to the necessity of special elaboration of the notion "residual schizophrenia". All these postulates are illustrated by the appropriate statistical population characteristics.