Oncocytoma includes 3-5% of all renal tumors. It does not manifest itself by typical symptoms and often is diagnostically confirmed in coincidence with examinations of other diseases. The preoperative diagnosis of oncocytoma is difficult. Oncocytoma must be taken into consideration in cases of bilateral multilocular tumors of the kidney. Neither RTG, USG and CT examinations, nor angiography give the specific picture of oncocytoma. One of the possibilities of diagnosis confirmation is the peroperative biopsy. If the latter confirms the diagnosis, then according to possibilities, operation with maintenance of unimpaired renal parenchyme should be performed. The prognosis of the disease is good and depends on the stage of cellular differentiation of tumor. The study presents observations of 4 patients subdued to surgery at the Urologic Clinic FHwP in Kosice since 1981 to 1990. The patients survive without metastases for 3-4 years.