Sera of 426 adult persons were examined to assess the prevalence of SEN virus (SENV) infection in Slovakia and to determine the importance of different risk factors for parenteral transmission. SENV prevalence was determined by the PCR method using primers of SENV-D and SENV-H strains. Positive results were found in 10 of 37 patients with acute hepatitis of unknown etiology, 7 of 38 with acute hepatitis B, 17 of 44 with chronic hepatitis B, 29 of 102 with chronic hepatitis C, 36 of 72 hemodialysis patients, 2 of 33 health care workers and 24 of 100 persons from the control group. The highest prevalence of SENV was among hemodialysis patients, significantly higher than in the groups of health care workers, acute hepatitis B and controls. The lowest prevalence was in health care workers group, significantly lower also in comparison with groups of chronic hepatitis B and C. Among the possible risk factors of virus transmission the average duration of hemodialysis (1.15 vs. 0.50 years), number of surgeries (1.60 vs. 1.10) and transfusions (1.34 vs. 0.94) showed notable differences in terms of SENV infection. Bilirubin and aminotransferase levels did not differ between SENV-positive and -negative groups. No pathogenetic role of SEN virus in liver injury was confirmed.