The primary aim of this study is to evaluate the safety and efficacy of solid organ transplantation in people with HIV disease by conducting a prospective, multi-center cohort of HIV-positive (+) patients who undergo kidney o liver transplantation. Our long-range goals are: (1) to provide patients and clinicians with information regarding the HIV-specific risks of transplantation, (2) to provide clinicians with information necessary to manage immunosuppressive and antiretroviral (ARV) medications together, and (3) to understand underlying basic science mechanisms that explain patient outcomes so that clinical management can be adjusted to maximize the outcomes. Patients with HIV infection are at significant risk for end stage organ disease. Prior to the advent of highly active antiretroviral therapy (HAART), such patients were often not considered as transplant candidates based on poor prognosis. However, with the use of HAART, HIV positive patients have experienced significant improvements in morbidity and mortality. Thus, increasing numbers of HIV+ patients with end stage kidney and liver disease are potential candidates for transplantation. Despite increasing referrals, patients and clinicians lack the necessary data to determine the safety and efficacy of transplantation and immunosuppression in this group. This lack of conclusive data has led to continued denial of care by many transplant centers and third party payers, resulting in frustration and confusion for both patients and their health care providers. Therefore, the primary clinical focus of this proposal is the design of a multi-center study that is powered to test the hypothesis that HIV+ liver and kidney transplant recipients will have patient and graft survival rates equivalent to other patient groups without HIV infection currently considered acceptable transplant candidates. In addition to providing the numbers required for a sufficiently powered study, the multicenter study provides access to 16 transplant centers for HIV+ patients facing end stage organ disease, facilitating regional access to avoid the logistic difficulties associated with limited access to distant sites. Of equal importance, the research plan establishes a prospective cohort that provides an ideal opportunity to explore mechanisms underlying disease progression in HIV+ transplant recipients and key issues in their medical management. The multi-center approach will capitalize on access to experts in the fields of virology and immunology. These investigators will explore the effects of immunosuppression (IS) on progression of HIV and viral co-pathogens known to be important in both transplant recipients and people with HIV infection. Progression of HIV and viral co-pathogens will be correlated with changes in the host immune response to HIV, viral co-pathogens, and allografts. These data will provide an essential contribution to an understanding of the factors that may be responsible for variations in graft and patient survival rates. This cohort will also provide the basis for describing the pharmacokinetic interactions between IS and the hepatically-metabolized ARVs, data that will greatly benefit health care workers managing HIV+ patients following transplantation, as maintaining appropriate levels of both of these classes of drugs will be essential for success.