Objective: Hepatitis A, a leading cause of enterically transmitted acute viral hepatitis throughout the world, has changed its pattern in developing countries. The objective of this study is to determine the current seroprevalence of hepatitis A virus (HAV) for different age groups in Istanbul, Turkey. Material and Methods: Serum samples of 3,868 patients, which had been previously taken, were used to determine anti-HAV IgG levels by the microparticle enzyme immunoassay (MPEIA) method (Architect SR i1000 and i2000, Abbott Diagnostics, Germany) between January 2011 and December 2013. Results: The prevalence of total anti-HAV antibodies was 64.8% for all patients. Among the 3,868 serum samples tested, 54% were from male patients and 46 % were from female patients. Seropositivity rates among the age groups were determined and anti- HAV antibody positivity rates were 55% for the 0-16 age group; 47% for the 17-30 age group; 73.5% for the 31-45 age group and the seroprevalence increased significantly from 50% (972/1944) in 0 to 30 years old to 89% in patients older than 46 years. Conclusion: The low seronegativity rates in young adults, show this group to be at high risk of acquiring an HAV infection. The results support the routine vaccination of children and the seronegative young adults against HAV.