Hepatitis B is a severe disease when acquired during the neonatal period. The identification of the infected pregnant women allows prevention of newborn infection by active and passive immunization soon after birth. We studied pregnant women in their first visit to eight different primary medical centers in Butantan, a subdistrict of S. Paulo city. 477 samples were tested for anti-HBc. From 44 (9.2%) anti-HBc positive samples, 2 (0.4%) were HBsAg positive and 37 (7.7%) were anti-HBs positive. A risk factor for hepatitis B could only be detected in 8 (18.9%) of the 44 anti-HBc positive samples