INTRODUCTION: Extended Criteria Donors (ECD) after Brain Death and uncontrolled Donors after Cardiac Death (DCD) have higher risk of Primary Nonfunction (PNF) and Acute Tubular Necrosis (ATN) and have become > 60% of our current deceased donors. Utility of Pre and Post-transplant Renal Resistance (RR) Index to Evaluate Organ Viability is described. METHODS: Retrospective analysis of 42 uncontrolled DCD and 24 ECD kidneys transplanted from 2009 through 2012, all preserved with RMP. Grafts with clinical criteria and biopsy proven ATN were analyzed. Correlation between RR obtained after 6 hours preservation with RMP and RR measured with Doppler Ultrasound (DU) 24 hours post-grafting was assessed. RESULTS: ECD kidneys had a lower RR with RPM than DCD kidneys (0.22 v 0.29 mmHg/mL/min; p=0.02). However, no differences were found among these groups regarding RR with US (0.78 v 0.73; p=0.12). ATN was more frequent in DCD vs EDC (77% vs 31%: p<0.001) with 86% of biopsy proven ATN in DCD. PNF due to venous thrombosis was present in 2 DCD kidneys. Simple linear regression failed to prove a significant degree of correlation between pre and post-transplant RR (p=0.76). CONCLUSIONS: RR is used to evaluate the renal hemodynamics and decide pre transplant organ suitability and orientate organ functionality after transplantation, however they are neither correlated nor able to predict ATN specially in DCD. RR obtained with RMP, as a calculation from direct measurement of renal flow and pressure, would produce a selection bias, considering that only kidneys with low RR (<0.4) are deemed acceptable rejecting those with higher RR and perhaps more risk of ATN. Additionally, in vivo assessment of RR with US can be affected by many clinical variables and only periodic follow-up of US morphology and blood flow can suggest ATN. Perhaps other markers of isquemic damage can be more efficient to predict ATN than hemodynamic approach. The different environments in which these measures are taken may be accountable for these result.