Objective: This study was undertaken to investigate the prevalence of HBsAg, anti-HBs and anti-HCV positivity in Istanbul, Turkey. Subjects and Methods: The frequencies of HBsAg, anti-HBs and anti-HCV positivity were determined in 1,157 randomly selected patients attending the outpatient clinic of Istanbul University Hospital, Istanbul, Turkey, during the years 1998 and 2001. All patients underwent complete physical and various routine laboratory examinations. Results: Of the 1,157 patients, the prevalence of HBsAg, anti-HBs and anti-HCV was 6.6, 28.1 and 2.4%, respectively. It appeared that having dental and surgical procedures formed the risk factors for HBV infection. HBsAg positivity in the health care workers was not different from that of the other professions, but anti-HBs was significantly higher in this group. Conclusions: Our findings indicate that HBV infection occurs more frequently than HCV in Istanbul, and this poses an important health problem in the community.