Background: Replication of genome-wide association study (GWAS) loci for schizophrenia in different populations as well as the study of their specificity for disease are important issues in searching for genetic factors of schizophrenia. The aim of the study: To search for the association of ZNF804A rs1344706 polymorphism with schizophrenia and schizoaffective disorder (SAD), as well as with clinical characteristics of these diseases, which are of prognostic value. Materials and methods: The study included 1458 patients diagnosed with schizophrenia (n=1284) or SAD (n=174) and a control group of healthy people (n=1051). Age-at-disease onset and the total score on the Positive and Negative Syndrome Scale were used to assess the severity of disease. Genotyping was performed using the restriction fragment length polymorphism technique. Results: There is an increase in the frequency of the risk genotype AA in the total group of patients compared to the control group (p=0,03, OR 1,31, CI 95% 1,03-1,7). An analysis of association between ZNF804A rs1344706 and clinical characteristics reveals a significant effect of genotype (p=0,007) on the severity of the disease measured with the Positive and Negative Syndrome Scale. The highest scores are in the group of genotype AA carriers and the lowest in the group of CC genotype carriers. No association between genotype and age-at disease onset was identified. Conclusion: The results confirm the earlier findings that the risk genotype AA of ZNF804A rs1344706 polymorphism is associated with schizophrenia and its severity.