New-onset hepatitis B (de novo B) after liver transplantation (OLTX) is an emerging concern. The goals of our study were to determine the incidence and pattern of this infection, to attempt determination of risk factors and the role of immunosuppression, and to review its morbidity/mortality. Over a 10-year period, 1078 OLTX were performed in 956 patients at our institution. Eight hundred twenty-six patients had proven negative hepatitis B surface antigen (HBsAg) before transplantation. Among these, 14 patients (1.7%), 8 women and 6 men, ages 21-59 years (median, 42 years), developed positive HBsAg after transplantation and were defined as de novo B. In 10 of 14 patients (71%), positive HBsAg was revealed during routine annual visits, whereas 4 patients had titer verification prompted by illness. Blood product use (cryoprecipitate, fresh-frozen plasma, platelets, and packed red blood cells) during the transplant hospitalization was similar between groups. Pretransplant hepatitis C infection was more prevalent among the 14 patients with de-novo B (7 of 14, 50% v 129 of 812, 16%; P < or = 05). Hepatitis B vaccine had been given to 12 patients (86%) (but not given to 2) who developed de novo B. Incidence and severity of rejection were similar in both populations, although de novo B patients had more late rejections. Our use of immunosuppressive protocols was the same in both groups. Mean follow-up of the infected patients is 24 (5-51) months. Twelve of these 14 de novo B patients were not clinically ill, with normal or near-normal transaminase levels. One of 14 has died from complications related to hepatic artery revascularization, and another is well after repeat OLTX for biliary strictures. Half of these de novo B patients remain free from viral antigens in their transplanted liver tissue. The high percentage of positive hepatitis C patients who acquire de novo B may indicate a link between these two viral infections and potential risk factor for de novo B. The origins of this infection are most likely multifactorial, needing further study. De novo B after liver transplantation is preliminarily associated with little clinical morbidity and mortality.