Authors studied 1013 first- and second degree relatives in families of 193 probands. The probands were stratified by clinical diagnosis into 6 groups: 1) nuclear variant of schizoaffective psychosis (SAP); 2) "marginal" (intermediate) variant of SAP; 3) schizoaffective variant of schizophrenia; 4) recurrent schizophrenia; 5) attack-like progressive schizophrenia; 6) bipolar affective disorder or manic-depressive psychosis (MDP). Probands (n=109) and their relatives were studied using the direct clinical examination; the study of 84 probands and their relatives was based on the medical records from the genetic archive of Mental Health Research Center, Russian Academy of Medical Sciences. Mental pathology was found in 72,5% of relatives; 27,5% were healthy. Prevalence of endogenous and non-endogenous psychoses, personality disorders and cases of alcoholism and suicides in the families of probands was studied. A "set" of these psychopathologies was similar in families of all probands and their frequency was higher than that in the general population that confirmed the affiliation of SAP with endogenous diseases by genetic characteristics. In patients with SAP, hereditary characteristics differed by the frequency, correlation and preference of some types of mental pathology compared to families of patients with schizophrenia and MDP, in particular, hereditary characteristics of patients with recurrent schizophrenia and MDP which were identified with SAP by many authors. The clinical-genetic patterns revealed in the study are considered as an argument for nosological independence of SAP.