Purpose: The RENAL nephrometry score (RNS) was developed to quantify complexity of renal tumors in a reproducible manner. We aim to determine whether individual categories of the RNS have different impact on the warm ischemia time (WIT) for patients undergoing robotic partial nephrectomy (RPN). Methods: In a retrospective analysis of a prospectively maintained database, we identified 251 consecutive patients who underwent RPN between January 2007 and June 2010. RNS was determined in 187 with available imaging. Univariable analysis and multivariable linear regression analysis were performed to identify which factors were more significantly associated with WIT. Results: Overall RNS was of low (4-6), moderate (7-9), and high complexity (10-12) in 84 (45 %), 80 (43 %), and 23 (12 %) patients, respectively. There was no association between gender (p = 0.6), BMI (p = 0.3), or anterior/posterior location (A) (p = 0.8), and WIT. On univariable analysis, longer WIT was associated with size (R) >4 cm (p < 0.0001), entirely endophytic properties (E) (p = 0.005), tumor <4 mm from the collecting system/sinus (N) (p < 0.0001), and location between the polar lines (L) (p = 0.004). Total RNS and WIT were highly correlated (Spearman correlation coefficient = 0.54, p < 0.0001). There was a significant trend of higher WIT with increased tumor complexity (p for trend <0.0001). After multivariable analysis, only R (p = 0.0003), E (p = 0.003), and N (p = 0.00002) components of the RNS were significantly associated with WIT. Conclusions: The A and L subcategories of the RNS have no significant impact on the WIT of patients undergoing RPN. WIT is significantly dependent upon the other subcategories, as well as the overall RNS. These findings can be used to preoperatively predict which tumor characteristics will likely affect WIT and may be useful in preoperative counseling as well as planning of approach.