ABSTRACTPurpose:To explore the association of body mass index (BMI) and comorbidity with renal function after nephrectomy.Materials and Methods:We retrospectively analyzed 263 patients submitted to partial or radical nephrectomy from 2000-2013. Variables assessed included BMI, Charlson Comorbidity Index (CCI), race, tobacco use, tumor histology, surgical approach, Fuhrman nuclear grade, and tumor (T) classification. Glomerular filtration rate (GFR) was estimated using the Cockroft-Gault equation, adjusted for gender. Logistic regression was performed and included all interaction terms.Results:Median follow-up was 19.6 months (IQR 5.2, 53.7). Median preoperative GFR was 86.2mL/min/1.73m2 and median postoperative GFR was 68.4mL/min/1.73m2. BMI (OR 1.07, 95%CI 1.02-1.11), CCI (OR 1.19, 95%CI 1.04-1.37), and radical nephrectomy (OR 3.09, 95%CI 1.51-6.33) were significantly associated with a decline in renal function of ≥25%.Conclusion:BMI and CCI are associated with postoperative decline in renal function after nephrectomy. Additionally, radical nephrectomy is significantly associated with decreasing renal function compared to partial nephrectomy. These findings highlight the importance of assessing patient comorbidity in the decision making process for patients presenting with a renal mass.