OBJECTIVE To investigate the time-dependent changes of estimated glomerular filtration rate (eGFR) after radical nephrectomy (RN) and partial nephrectomy (PN) for renal cell carcinoma (RCC) and to determine the risk factors for the new onset of a postoperative eGFR <60 ml/min/1.73 m(2). METHODS We assessed the renal function of 253 RCC patients by using the eGFR, and investigated the time-dependent changes of the eGFR after the operation. Regression models were used to determine risk factors for the new onset of an eGFR of <60 ml/min/1.73 m(2) in 211 patients who had at least one month of postoperative follow-up. RESULTS From the first postoperative day to the 60th postoperative month the eGFR in the RN group was significantly lower than that in the PN group. For patients who had at least 1 month of postoperative follow-up, multivariable analysis revealed that RN (p < 0.001), age (p = 0.028), and maleness (p = 0.013) were risk factors for the postoperative onset of an eGFR <60 ml/min/1.73 m(2). CONCLUSIONS Renal function after PN was better than that after RN, and RN was a greater risk factor for the postoperative onset of an eGFR <60 ml/min/ 1.73 m(2).