We performed a retrospective serologic survey of 583 organ donors and 1043 transplant recipients for antibodies to human immunodeficiency virus type 1 (HIV-1). Two (0.34%) of the 583 donors and 18 (1.7%) of the 1043 recipients had HIV-1 antibodies by enzyme immunoassay and by Western blot. Two of 5 seropositive recipients tested also had blood cultures positive for HIV-1. Seven (0.7%) of the 1043 transplant recipients had antibodies to HIV-1 before transplantation; 2 of these had hemophilia A, and 5 had previous transfusions. Eleven (1.3%) of 860 recipients followed for 45 days or more seroconverted to HIV-1 a mean of 96 days after transplantation. Likely sources of HIV-1 infection for 3 of these 11 recipients included a seropositive organ donor in 1 patient and high-risk blood donors in 2 patients. A definite source of HIV-1 infection was not found for the other 8 recipients, 3 of whom seroconverted to HIV-1 after institution of blood donor screening for HIV-1 antibodies. Seroconversion to HIV-1 was less common in kidney recipients than in liver, heart, or multiple-organ recipients (P less than 0.02). Nine (50%) of the 18 HIV-1 seropositive transplant recipients died a mean of 6 months after transplant surgery, and 9 (50%) are still alive a mean of 43 months after transplantation. AIDS-like illnesses occurred in 3 of the dead and 1 of the living patients and included pneumocystis pneumonia (3 cases), miliary tuberculosis (1 case), and recurrent cytomegalovirus infection (1 case). These data suggest that the course of HIV-1 infection is not more severe in transplant recipients receiving cyclosporine than in other hosts and that, despite screening of blood and organ donors, a small number of transplant recipients will become infected with HIV-1.