Exclusion of liver grafts from hepatitis B core antibody (anti-HBc) positive donors to prevent de novo hepatitis B virus (HBV) infection after liver transplantation is not feasible in areas highly endemic for HBV virus like Taiwan, where approximately 80% of adults are anti-HBc(+). The efficacy of lamivudine monotherapy to prevent de novo HBV infection after living donor liver transplantation (LDLT) using grafts from anti-HBc(+) donors remains to be elucidated. From June 1994 to August 2000, LDLT was performed in 42 recipients. Twenty-four of the 42 donors were anti-HBc(+) (57%). Pre-transplant HBV vaccination was given to all recipients irrespective of anti-HBc status at monthly intervals for 3 months. Until December 1997, eight recipients received liver grafts from anti-HBc(+) donors without prophylaxis. Since January 1998, prophylaxis with lamivudine monotherapy was given to 16 recipients receiving liver grafts from anti-HBc(+) donors. De novo HBV infection occurred in three of the eight recipients (37.5%) who did not receive prophylaxis, while none of the 16 recipients given lamivudine developed de novo HBV infection after a mean follow-up of 25 months. Two of the three recipients with de novo HBV infection were anti-HBs(-) and one recipient was anti-HBs(+). Lamivudine was well tolerated, and no side effects were noted. These results suggest that lamivudine monotherapy for recipients receiving anti-HBc(+) liver grafts is a simple, relatively inexpensive and effective prophylactic regimen for prevention of de novo HBV infection. The additive protection provided by vaccine-induced or natural immunity is uncertain.