Diagnosing the acquired immunodeficiency syndrome (AIDS) in transplant recipients can be difficult due to the patient's medication-induced immunosuppressed state. We report two renal allograft recipients who acquired HIV infection at the time of transplantation and later went on to develop multiple opportunistic infections. Careful documentation of HIV antibody status of the donor and recipient, when available, the nature of immunosuppressive therapy used, the type of infections and their timing after transplantation, as well as the patient's absolute T4 lymphocyte count, T cell ratio, and B cell humoral response to infection were used as factors to distinguish between infection related to immunosuppressive therapy and that seen in HIV-induced immunodeficiency. Reduction in immunosuppressive therapy because of the HIV-related immunodeficiency state did not result in allograft rejection. Both patients died of their multiple infections. The determination of AIDS in the transplant recipient has both therapeutic and prognostic significance. This diagnosis should be considered when transplant patients develop unusual infections in relationship to their posttransplant course.