Renal oncocytoma is a benign tumour that can be associated with renal cell carcinoma in rare genetic syndromes. The authors report the case of a 62-year-old patient with no medical history, in whom assessment of low back pain in 1999 demonstrated a 40 mm tumour of the lower pole of the left kidney. Percutaneous needle biopsy of the tumour demonstrated oncocytoma confirmed by Hale's stain. Follow-up ultrasound demonstrated an increase in size (88 mm) and a nine-fold increase in volume over four years (210 cm3 in April 2003). Surgery was indicated in view of the rapid increase of the tumour volume. Histological examination of the operative specimen demonstrated a combination of oncocytoma and Fuhrman grade III renal cell carcinoma.