To analyze to what extent partial nephrectomy (PN) is superior to radical nephrectomy (RN) in preserving renal function outcome in relation to tumor size indication.Clinical data from 973 patients operated at 9 academic institutions were retrospectively analyzed. Glomerular filtration rate (GFR) before and after surgery was calculated with the abbreviated Modification of the Diet in Renal Disease equation. For a fair comparison between the 2 techniques, all imperative indications for PN were excluded. A shift to a less favorable GFR group following surgery was considered clinically significant.Median age at diagnosis was 60 years (19–91). Tumor size was smaller than 4cm in 665 (68.3%) cases and larger than 4cm in 308 (31.7%) cases. PN and RN were performed in 663 (68.1%) and 310 (31.9%) patients, respectively. In univariate analysis, patients undergoing PN had a smaller risk for developing significant GFR change following surgery than those undergoing RN did. This was true for tumors≤4cm (P = 0.0001) and for tumors>4cm (P = 0.0001). In multivariate analysis, the following criteria were independent predictive factors for developing significant postoperative GFR loss: the use of RN (P = 0.0001), preoperative GFR<60ml/min (P = 0.0001), tumor size≥4cm (P = 0.0001), and older age at diagnosis (P = 0.0001).The renal function benefit carried out by elective PN over RN persists even when expanding nephron-sparing surgery indications beyond the traditional 4-cm cutoff.