The investigation involved 25,891 blood donors who attended for the first time the Blood Center of Ribeirão Preto, Brazil, between Jun 23, 1996 and Jun 22, 2001. The objective was to study the proportion of positive serological markers for hepatitis B and C at the initial screening tests and to estimate the prevalence of such infections through the analysis of confirmatory tests, carried out at the University Hospital as a part of the patients evaluation. Data from the donors and laboratory results were obtained from the records of both the Blood Bank and the Hospital. The population of donors was mainly composed by males (83.6%) and by individuals between 26 and 45 (64%) years of age. The proportions of positive results in screening tests were 0.6% (CI95%: 0.54-0.72) for HBsAg and 1.2% (CI95%: 1.02-1.28) for anti-HCV. Confirmatory testes showed values of prevalence of 0.2% (CI95%: 0.16-0.28) for hepatitis B and 0.3% (IC95%: 0.24-0.38) for hepatitis C.