Renal oncocytoma is a benign (noncancerous) growth of the kidney. Renal oncocytoma generally do not cause any signs or symptoms and are often discovered incidentally (by chance) while a person is undergoing diagnostic imaging for other conditions. Some people with Renal oncocytoma will have abdominal or flank pain; blood in the urine; and/or an abdominal mass. Although these tumors can occur in people of all ages, they most commonly develop in men who are over age 50. The exact underlying cause of most isolated (single tumor affecting one kidney) Renal oncocytomas is unknown. Multiple and bilateral (affecting both kidneys) Renal oncocytomas sometimes occur in people with certain genetic syndromes such as tuberous sclerosis complex and Birt-Hogg-Dube syndrome.