This study examines Diagnostic Related Group (DRG) day outliers among End Stage Renal Disease (ESRD) patients enrolled in Medicare´s ESRD Program. Day outlier hospitalizations are cases that remain in the hospital longer than a specified period of time defined by HCFA. The study uses a sample of hospitalizations from the United States Renal Data System. OBJECTIVE: The objectives of the study are to describe the portion of the ESRD population which is most likely to be hospitalized, to examine the distribution of ESRD patients within DRGs, and to identify variables significantly related to DRG day outlier status. METHODS: This study has a retrospective cohort design. To describe the hospitalized segment of the Medicare ESRD population, frequency distributions of patient characteristics are reported. To identify variables which are predictors of DRG day outlier status, a logistic regression is performed. RESULTS: Day outlier hospitalizations represented 3.9% of all hospitalizations by ESRD patients (n=3,921,883). This study shows that White males between the age of 60 and 99 years; with less than a year since their first ESRD service; with admission to MDCs 22, 24 or the DRGs not associated with an MDC; with lung cancer, leukemia, malnutrition or liver conditions as comorbidities are most likely to have day outlier hospitalizations. CONCLUSIONS: The findings of this study can aid in identifying patients more likely to benefit from disease management programs specifically designed to address the needs of this population. Other benefits possible benefits are an increase in the patient´s quality of care, quality of life, as well as an overall increase in health outcomes.