The SEN virus has been tentatively linked to transfusion-associated non-A to E hepatitis. The aim of the present study was to 1) determine the prevalence of SEN virus among Egyptian patients with hepatitis C virus (HCV)-related chronic liver disease and patients undergoing hemodialysis and 2) demonstrate the clinical effect of SEN virus infection on coexistent hepatitis C in terms of severity and probability of developing hepatocellular carcinoma. Polymerase chain reaction was used to detect SEN virus-D and SEN virus-H DNA in serum samples of 74 patients with HCV-related chronic liver disease, 45 uremic patients undergoing maintenance hemodialysis, and 28 healthy controls. SEN virus-D/H DNA was detected in 13.5% of patients with chronic liver disease, 11.1% of patients undergoing hemodialysis, and 7.1% of healthy controls, with no significant differences between patients and the control group. Clinical and biochemical measures did not significantly differ between SEN virus-infected and noninfected patients in the chronic liver disease group or the hemodialysis group. The rate of SEN virus infection was significantly higher in patients with chronic liver disease and hepatocellular carcinoma (33.3%) than in those with chronic liver disease only (8.5%) (P < .05). In conclusion, SEN virus does not seem to be a common infection in Egyptian patients. It has no apparent influence on the severity of coexistent HCV-related chronic liver disease but could be a risk factor for hepatocellular carcinoma in such patients. Further studies are needed to define the etiopathogenic role of SEN virus infection in the development of hepatocellular carcinoma.