Renal parenchymal thickness was estimated by using CT in 360 patients with no evidence of renal disease. In each patient, the measurements were normalized to the transverse diameter of the vertebral body and a reference table was formulated. The renal parenchymal thickness decreases about 10% per decade of increasing age in both men and women. These findings are consistent with previously reported findings based on autopsy material. The proposed table may be useful as a criterion for assessing normal renal parenchyma on CT.