Pre- and post-nephrectomy kidney growth was studied by computed tomography (CT) in 32 patients with contralateral renal cancer. Kidney enlargement was assessed by comparing the size of the unaffected kidney, in 32 pre- and 61 post-nephrectomy CT examinations, with the corresponding normal size, determined from 120 CT examinations of binephric individuals with no renal disease. The unaffected kidney was found to be 36% larger 1 month before nephrectomy and 54, 62 and 47% in the 1st, 2nd, and 3rd postoperative year, respectively. Compensatory renal growth was influenced both by contralateral cancer and nephrectomy and did not depend on the patient's age or sex.