Abstract.A cross-sectional survey of the seroprevalence of hepatitis B virus (HBV) markers among healthy people was conducted in San Juanito, a rural community in the northern state of Chihuahua, Mexico. The overall prevalence in 970 people was 6.6% for antibody to hepatitis B core antigen. There was an age effect on the prevalence of HBV infection, and a gradual increase in prevalence was observed in patients up to the age of 40 years. Those subjects with a history of dental procedures had a 2-fold higher risk for HBV infection (odds ratio [OR], 2.4; 95% confidence intervals [CI], 1.01-5.86), and there was a 74% increased risk for each blood product transfusion (OR, 1.74; 95% CI, 1.09-2.77). Horizontal transmission seems to be the major source of endemicity in San Juanito because no woman was a chronic carrier. To lower HBV transmission rate, an adequate active screening program for blood donors should be implemented, together with a universal infant immunization program.