We performed a case-control study to evaluate the association of a new human DNA virus named TT virus (TTV) with hepatocellular carcinoma (HCC). We recruited 174 subjects hospitalized for HCC (84% males; mean age: 64 years) and 118 patients hospitalized for non-liver diseases in Brescia, northern Italy, as controls (94% males; mean age: 66 years). TTV DNA was found in serum by polymerase chain reaction (PCR) in 26 cases (15%) and 11 controls (9.3%) (P >. 1). TTV group 2 infection was identified in 16 cases (61.5%) and 4 controls (36.4%) (P >.1) using a type-specific PCR method. Sequence analysis of 222 nt of TTV DNA demonstrated that the remaining 10 cases and 7 controls were all infected by group 1. The odds ratio (OR) for TTV-DNA positivity, adjusted for demographic variables, hepatitis B surface antigen (HBsAg), hepatitis C virus (HCV) RNA, and heavy alcohol intake was 1.8 (95% CI: 0.7-4.8; P >.1). The OR did not change when the analysis was restricted to 14 HCC cases and 56 controls who were negative for each known risk factor for HCC (OR = 1.7; 95% CI: 0.8-4.0). TTV-DNA positivity was not associated with transfusion history. The prevalence of TTV DNA was higher among HCC cases positive for HBsAg (10 of 38 [26.3%]) than among those positive for HCV RNA (8 of 62 [12.9%]) or negative for hepatitis B virus (HBV), HCV, and hepatitis G virus (HGV) infections (5 of 62 [8. 1%]) (P =.02). This study does not support the hypothesis of an association between TTV infection and HCC.