Introduction/Objective: Robotic-assisted partial nephrectomy (RPN) offers a mean length of stay (LOS) of 2 to 3 days. The purpose of this study is to determine the impact of modifiable and nonmodifiable risk factors on hospital LOS after RPN. Patients and Methods: We retrospectively reviewed our prospectively maintained database to identify all patients undergoing RPN for localized tumors at five US centers from 2007 to 2013. Patient and tumor characteristics were compared among hospital LOS groups. Associated factors were modeled using univariate and multivariate cumulative logistic regression to determine factors predictive of hospital LOS. Results: One thousand five hundred thirty-two patients were grouped into LOS 1 to 3 days (1298, 84.1%), LOS=4 days (133, 8.6%), and LOS >4 days (110, 7.2%). Patient demographics were similar between groups. Patients in the LOS=4 and LOS >4 day groups were more likely to have a higher Charlson comorbidity index score (mean 2.2, 3.1 and 3.8; p<0.001), higher nephrometry score (mean 7.1, 7.6, 7.8; p=0.0002), and larger tumors (mean 2.9, 3.6 and 3.5 cm; p<0.0001) than those in the LOS 1 to 3 day group. Significant differences in complication rates were observed when comparing LOS 1-3 (116, 8.9%), LOS=4 (40, 30%), and LOS >4 (59, 54%). According to the Clavien-Dindo classification of surgical complications, 11 grade 3 and 11 grade 4 complications occurred in patients with an LOS of 4 or more days (p<0.0001). Postoperative transfusion, deep vein thrombosis, pulmonary embolism, atrial fibrillation, dyspnea/atelectasis, ileus, and acute renal failure each significantly predicted a hospital LOS >4 days (p<0.001). Conclusion: 15.8% of patients undergoing RPN have an LOS of 4 days or more. Longer LOS was independently associated with higher Charlson index, nephrometry score (nonmodifiable factors), and perioperative complications (potentially modifiable). These data may be useful in perioperative counseling and payer precertification.