The aim of the trial was to study compensatory potential of renal parenchyma in the presence of renal cell carcinoma (RCC) and after organ-saving and radical surgical treatment as shown by one-photon emission computed tomography (OPECT). OPECT before the treatment and 6 and 12 months after it evidences that in unilateral RCC, irrespective of the focus location, both kidneys as a single organ respond to tumor growth with compensatory hypertrophy. Compensatory reserve is limited. In tumor size more than 6 cm the affected kidney starts losing the volume of the functional tissue while infiltrative growth is most likely. Assessment of the compensatory potential of the kidneys provides additional information. If the volumes of the kidneys differ by more than 30%, RCC growth is infiltrative. In this case only radical nephrectomy is recommended. If the size of the kidneys is by 60% more than normal one and parenchymas of the affected and contralateral kidney reach their compensatory limit but are equal, indications to organ-saving surgery extend as greater hypertrophy of the remaining kidney is excluded. After organ-saving surgery, a compensatory increase was observed in the contralateral kidney. This is explained by effective distribution of protein material and separate processes of proliferation (healing) and hypertrophy (compensation). Assessment of anatomo-functional condition of renal parenchyma helps better selection of patients for organ-saving surgery.