OBJECTIVE We analyze the relationship among various patient, operative and tumor characteristics to determine which factors correlate with renal parenchymal volume loss after nephron sparing surgery using a novel 3-dimensional volume assessment. METHODS We conducted a retrospective review of an institutional database of patients who underwent nephron sparing surgery from 1992 to 2014 for a localized renal mass. Tumors were classified according to the R.E.N.A.L. nephrometry system. Using 3-dimensional reconstruction imaging software, preoperative and postoperative renal parenchymal volume was calculated for the ipsilateral and contralateral kidney. RESULTS A total of 158 patients were analyzed. Mean patient age was 58.7 years and mean followup was 40.1 months. Mean preoperative tumor volume was 34.0 cc and mean tumor dimension was 3.4 cm. Mean R.E.N.A.L. nephrometry score was 6.2, with 60.1%, 34.2% and 5.7% of tumors classified as low, medium and high complexity, respectively. Mean change in renal parenchymal volume after nephron sparing surgery was -15.3% for the ipsilateral kidney and -6.8% for total kidney volume. On univariate analysis ischemia time, tumor size, R.E.N.A.L. nephrometry score, complexity grouping and the individual nephrometry components of tumor size, percent exophytic, anterior/posterior, depth and tumor proximity to the renal artery or vein were associated with greater renal parenchymal volume loss. On multivariate analysis only ischemia time, tumor size, posterior location and percent exophytic were independently associated with more renal parenchymal volume loss. CONCLUSIONS Using precise 3-dimensional volumetric analysis we found that ischemia time, tumor size and endophytic/exophytic properties of a localized renal mass are the most important determinants of renal parenchymal volume loss.