The State of Amazonas in the Brazilian Amazon region is an area of high prevalence of hepatitis B and D virus (HBV and HDV) infection. The aim of this study was to identify epidemiological patterns and risk factors of HBV and HDV infections in Barcelos, in the basin of the Negro river. A random sample (798 in all) of the total population in the urban area and in 2 rural villages was surveyed. A standardized questionnaire was used and blood samples were tested by enzyme-linked immunosorbent assay: 1.63% had hepatitis B surface antigen, 12.9% had anti-hepatitis B surface antibody and 21.4% had anti-hepatitis B core antigen. The overall prevalence of HBV infection was 24.6%. Anti-hepatitis D was present in 5 subjects, all of them non-natives, and hepatitis B e antigen in 2. A positive association between history of dental treatment with an unqualified dental surgeon was found (P < 0.05). These results suggest a low prevalence of HVB and HDV infection, in contrast with other parts of the Amazon area.