AIM: To specify trends in clinical and laboratory manifestations of virus hepatitis B and C (HBV and HCV) in patients with blood diseases from the moment of the first positive specific tests for HBV and HCV markers; to assess effects of HBV and HCV infection on efficacy of treatment of blood disease treatment, i.e. lifespan of patients with hematological diseases. MATERIAL AND METHODS: The study enrolled 257 patients: 205 with acute leukemia - AL, 40 with lymphoproliferative diseases, 4 - with CML and 8 - others; 8 healthy bone marrow donors. The patients were admitted to Russian Hematological Research Center in 2004-2006 Follow-up median was 253 days. A total of 7800 biological samples were studied, among them about 4000 tests for HBV DNA and HCV RNA. RESULTS: Positive tests for specific markers of HBV and HCV were absent only in 78 (29.4%) patients. Positive markers of coinfection were detected in 57 (32.8%) of 174 patients with HBV infection and in 81.4% of 70 patients with HCV infection. Probability of detection of HCV markers after positive tests for HBV markers and vice versa is about 3 times higher than probability of their isolated detection. Among patients infected with HBVsymptoms of hepatitis B are likely to appear in 56% patients to day 500 of follow-up from the date of the first positive specific test. Median of the interval between the first positive test for HBV markers and probable clinical signs of hepatitis was 30 days. Among patients with HCV infection, 85% develop hepatitis to follow-up day 300 since the date of the first specific positive test. Almost 100% patients infected with two viruses develop hepatitis to follow-up day 600. Median of the interval between the first positive test for HBV and HCV markers and probable hepatitis picture was 47 days. Overall 3-year survival of AL patients was 40%, of patients with lymphoproliferative diseases - 58%. Overall 7-month survival was 75% in AA patients. HBV infection in patients with blood disease is associated with high risk of death, especially in AA and AL. Association between HCV infection and survival is not proved. CONCLUSION: A high rate of clinical realization of viral hepatitis B and C, especially in coinfection, calls for virological and clinical monitoring of patients with any positive test for HBV and HCV markers.