Early rehospitalization following transplantation is a common and costly event among kidney transplant recipients (KTRs). While this outcome has been identified as a quality of care metric for hospitals by the Centers for Medicare & Medicaid Services, it is not known whether early rehospitalizations after kidney transplant represent preventable events. A national study of Medicare-covered recipients who underwent renal transplant in 2005 revealed that over half were rehospitalized in the first six months, at a cost o 339 million dollars to Medicare.1 Identifying risk factors for rehospitalization and developing interventions to prevent rehospitalization have been a focus of many studies in patients with a variety of diagnoses2 from congestive heart failure3 to pneumonia.4 In KTRs, however, few data exist about the specific patterns and causes of early (defined as <30 days) rehospitalization following kidney transplantation. The central premise of this grant is that give the substantial baseline risks of kidney failure and transplantation, only a minority of early rehospitalizations after kidney transplantation is preventable. We also hypothesize that early rehospitalization predicts future risk of later adverse outcomes including graft loss and death. We propose a retrospective cohort study of KTRs using detailed data from a single center. The study design will enable the applicant to achieve the following Specific Aims: 1) To determine categories of reasons for early rehospitalization after renal transplantation based on expert in-depth review, and to classify these causes according to preventability; 2) To determine predictors of early rehospitalization; and 3) To determine if early rehospitalization is an independent predictor of later adverse outcomes (mortality, graft loss). The results of this study have the potential to improve patient care after kidney transplantation by identifying important modifiable process-of-care factors that increase rehospitalization risk. We will develop a prediction model for early rehospitalization that we will externally validate in a cohort of KTRs a other transplant centers. We will also determine if early rehospitalization is an independent predictor of later allograft loss, as it may prove to be an easily measured prognostic tool for clinicians. The proposed research project will be in the context of completing the Masters of Science in Clinical Epidemiology degree at the University of Pennsylvania. The degree program encompasses intensive instruction on the fundamentals of epidemiology and analytic methods; this coursework will enhance and guide the research process of the applicant. The longer-term objectives of the applicant for this grant are to prepare presentations and manuscripts for publication, apply the results to the design of future prospective studies, and use this study as the foundation of a future K-award application.