OBJECTIVE Partial nephrectomy (PN) for patients with T1a renal cell carcinoma (RCC) has increasingly become accepted, although its role for patients with T1b RCC remains controversial. We retrospectively evaluated and then compared the oncologic and functional outcomes of patients with pT1b RCC who were treated with PN or radical nephrectomy (RN). METHODS A total of 70 patients who were diagnosed with pT1bN0M0 RCC between January 1995 and December 2004 were included. The 5-year overall survival (OS), the 5-year recurrence-free survival (RFS), and the 5-year cancer-specific survival (CSS) were compared between the groups. Preoperative and postoperative serum creatinine and estimated glomerular filtration rate (GFR) levels were analyzed to assess renal function. RESULTS The 5-year OS (92.3% vs. 87.8%, p=0.501), RFS (92.3% vs. 77.8%, p=0.175), and CSS (92.3% vs. 94.5%, p=0.936) of the PN and RN groups were not statistically different. The proportion of patients with decreased renal function was lower in the PN group than in the RN group (PN=0% vs. RN=11.5%). The postoperative change in serum creatinine and the GFR 1 year after nephrectomy was higher in the RN group than in the PN group (PN=0.2±0.2, 12.1±9.1 vs. RN=0.3±0.5, 18.1±12.5), but there was no statistical difference. CONCLUSIONS There were no statistically significant differences in prognosis or renal function between patients treated with PN and those treated with RN for pT1b RCC. PN may be a useful treatment modality for patients with pT1b RCC.