Transfusion-transmitted virus (TTV) is a recently discovered transfusion-transmissible DNA virus. Its frequency and clinical impact has not been established in cancer patients in Turkey. In this study, we determined the prevalence of TTV DNA positivity, and its relationship with history of transfusion, amount of transfusion, age and sex in patients with hematological and solid malignancies. Sixty-one patients (35 male and 26 female) followed up for various malignancies and 45 healthy subjects were included in the study. ITV DNA was assayed by the polymerase chain reaction (PCR). TTV DNA was detected in 18 of 61 patients (29.5%) and in 5 of 45 control subjects (11.1%). In cancer patients, the prevalence of TTV DNA positivity was higher to comparison with control group. In addition, the prevalence of TTV DNA positivity was significantly higher in 22 patients who had a history of blood transfusion in the last 6 months than 39 patients who had no current or past history of transfusion (40.9% vs 23.0% respectively). These results suggest that the prevalence of TTV DNA is high and the parenteral route is an important mode of transmission for TTV in cancer patients. In addition, the high prevalence and persistence of TTV in cancer patients with parenteral risk exposure could be related to the immunodeficiency due to cancer and high viral loads by parenteral route.