There is an increase in the number of patients with renal cell carcinoma (RCC) every year. At the same time radical nephrectomy (RN) remains the standard treatment of renal malignancies and the most common surgical procedure for this pathology. A considerable number of patients with kidney cancer have diminished renal function that worsens after removal of functioning kidney tissue together with a tumor. This promotes retained low overall survival rates in patients with RCC, by improving cancer-specific survival. Renal function was studied in 48 patients with RCC prior to and 1 year after RN. In all the patients, glomerular filtration rate (GFR) was estimated using the Cockroft-Gault equation with and without protein load. Renal parenchyma volume was calculated by spiral computed tomography. Patients aged over 60 years had decreased baseline renal function as compared to those aged under 60 years (GFR 77.4 versus 103.6 ml/min/1.73 m2). The postoperative reduction in female renal function was more pronounced (GFR, 84.92 versus 92.54 ml/min/1.73 m2). Patients with metastatic RCC had lower baseline renal function and its significant postoperative loss than those with the non-metastatic forms of a tumor. A load test showed a substantially decreased renal reserve in patients with RCC.