Organ-sparing renal surgery for renal cell carcinoma has greatly increased in importance over the last few years owing to the widespread application of ultrasound examination. When a normal contralateral kidney is present the indications for organ-sparing surgery are very strict. Our patient presented with a large tumour in a single kidney and, though fully informed about all the risks involved, insisted upon an organ-sparing operation. In planning and execution of the operation we were much assisted by the use of a three-dimensional reconstruction made from the CT scan carried out preoperatively, because this showed the exact position and size of the tumour. We report on the course of the patient's illness and present a simple three-dimensional reconstruction technique.