The clinical characteristics and outcome of posttransplantation aplastic anemia (AA) were determined in 12 of 1,736 patients (0.007%) undergoing orthotopic liver transplantation (OLT) that were afflicted with AA. None of the affected patients had a history of hematologic disease. Median patient age was 53 years (range, 2-61 years); 10 of the affected patients were men, and 2 were women. The etiologies of AA included non-A, non-B, non-C fulminant hepatic failure (FHF) (3 patients), graft-versus-host disease (4 patients), Parvovirus-induced (1 patient), and idiopathic (4 patients). The median duration between OLT and the onset of AA was 12 days (range, 11-14 days) in the 3 patients undergoing OLT for FHF; in contrast, AA developed in the other 9 patients at 37 days (range, 27-51 days) after OLT. Eleven patients were treated with reduction of their cyclosporine or tacrolimus dosage, granulocyte colony-stimulating factor, anti-thymocyte globulin, and Solumedrol. Two of the 3 patients developing AA following OLT for FHF achieved hematologic recovery 21 and 92 days after diagnosis. In contrast, all 9 non-FHF patients developing AA after OLT died, 5 due to infectious complications and 4 following intracranial bleeding. AA is an unusual complication of OLT. In the setting of FHF, it affects young males in the early posttransplantation period, and, when infectious complications can be avoided, remission and stable allograft function can be anticipated. However, in the non-FHF patient, AA occurs in older individuals later in the posttransplantation period and has a uniformly poor outcome.