Background/Aims: TT virus (TTV) is a unenveloped, single-stranded and circular DNA virus isolated from the serum of a patient with posttransfusion hepatitis of unknown etiology. We evaluated the prevalence, risk factors, and clinical significance of TTV in patients with chronic renal failure(CCRF) undergoing maintenance hemodialysis (HD). Methods: We examined TTV DNA in serum of HD-undergoing patients and healthy controls using the nested polymerase chain reaction. Results: TTV DNA was detected in 15 (20.0%) of 75 HD-undergoing patients and 10 (13.2%) of 76 healthy controls (p>0.05). The prevalence of TTV did not differ according to the duration of HD or transfusion history of the patients. The prevalence of TTV was higher in IgG anti-HBc positive patients than IgG anti-HBc negative patients (27.5% vs. 4.2%, p=0.03). There was no relationship between TTV infection and liver diseases. Conclusions: The prevalence of TTV infection in CRF patients undergoing HD was similar with that of healthy controls. These results suggest that TTV infection may share the route of transmission with HBV infection in adults. (Korean J Gastroenterol 2001;37:14-20)