Background and Aims: HEPATITIS G virus (HGV) has a worldwide distribution, and the prevalence rates among blood donors and high-risk groups are different. The purpose of this study was to assess the frequency of the HGV infection in blood donors as a blood borne pathogen and in high-risk groups (multitransfused patients), such as thalassemic, hemophillic, and hemodialysis patients. Methods: 400 Iranian (Tehran Blood Transfusion Center, 2004) blood donors were tested for HGV RNA by a reverse transcriptase chain reaction (RT-PCR) method. The participants were negative in blood screening tests for HEPATITIS B surface antigen (HBsAg), HEPATITIS C virus antibodies (anti- HCV), human immunodeficiency virus (HIV) Ag/Ab, and Rapid Plasma Reagin (RPR). HGV RNA positivity was surveyed in 40 thalassaemic, 16 hemophilic, and 46 hemodialysis patients by RTPCR. To assess the frequency of infection, the prevalence of HGV RNA positive cases per 100 donors/patients with 95% confidence intervals (95% CI) were calculated. P values were estimated with chi-square tests. Results: 19 (4.8%; 95% CI: 2.9-6.5%) out of 400 blood donors samples were HGV RNA positive. The prevalence of HGV infection was 5.28% (13 out of 243) in repeat donors, 4.12% (4 in 99) in lapsed donors, and 3.50% (2 out of 58) in first-time blood donors. The combined prevalence of HGV infection in these groups of patients was 16 (15.7%; 95% CI: 8.3-23.1%) out of 102 samples. HGV RNA frequency was 1 out of 40 (2.5%; 95% CI: 1.8-3.2%) thalassemic patients, 15 out of 46 (32.6%; 95% CI: 16.8-48.4%) hemodialysis patients, and 0 out of 16 hemophilics patients. Conclusions: The prevalence of HGV RNA in the high-risk population was 15.7% and nearly 3 times more than blood donors (4.8%). These data indicate the possibility of parenteral transmission of HGV, especially by transfusion of blood and blood components. Decisions to screen blood supplies for a transfusion-transmitted infection agent should be based on sufficient benefits for recipients.