Purpose: To report the prevalence of new-onset renal insufficiency in patients undergoing laparoscopic partial nephrectomy (LPN) as compared to laparoscopic radical nephrectomy (LRN) for pathologic T1a lesions. Patients and Methods: Forty-eight patients and 37 patients with a normal contralateral kidney, preoperative creatinine (Cr) concentration <2 mg/dL, and tumors <4 cm in size underwent LPN and LRN, respectively. Glomerular filtration rate (GFR) was estimated using an abbreviated Modification of Diet in Renal Disease (MDRD) equation. Cr concentrations and GFR values were analyzed in patients undergoing LPN or LRN. Statistical analysis was performed with two-tailed t-test assuming unequal variances, to establish significance by P < 0.05. Results: Preoperative Cr and GFR was equivalent in the LPN and LRN groups (0.9 mg/dL and 90 mL/min). At last follow-up (mean 205 and 233 days in the LPN and LRN groups, respectively) mean creatinine was 1.03 ± 0.3 mg/dL v 1.4 mg/dL ± 0.3 (P = 0.0002). Estimated GFR was 79 ± 22 mL/min per 1.73 m2 v 55 ± 14 mL/min per 1.73 m2 (range 31-91 mL/min per 1.73 m2; P < .0001) in the LPN and LRN groups, respectively. One patient in the LPN group and three patients in the LRN group had clinical renal insufficiency as defined by Cr > 2.0 mgdL. Subclinical renal insufficiency (Cr < 2.0, but calculated GFR <60 mL/min per 1.73 m2) was present in 57% of the LRN patients v 15% of the LPN patients. Conclusions: LPN preserves renal function more effectively than LRN for pathologic T1a lesions. Subclinical renal insufficiency (GFR <60 mL/min per 1.73 m2) was present in the majority of patients undergoing radical nephrectomy in our series. Importantly, this series included the use of warm ischemia in all cases.