In 27 patients nephrectomized for renal carcinoma, the compensatory hypertrophy of the remaining kidney was assessed by 72 CT examinations performed one month before and during 32 months after nephrectomy. Kidney size was estimated on CT by multiple measurements of the renal parenchymal thickness. Kidney growth was evaluated by comparing the amount of renal parenchyma before and after contralateral nephrectomy. Renal compensatory hypertrophy varied with postnephrectomy time. Kidney enlargement was 15% in the first 3 months, reached maximum 30% about a year later, and was reduced to 5%, 2 1/2 years postoperatively.