PURPOSE: To compare the ratio of renal cortical thickness to renal parenchymal thickness in early diabetic nephropathy and in normal control group. MATERIALS AND METHODS: We performed spiral CT in 17 patients suffering from diabetic nephropathy without renal failure or renal atrophy. The normal control group consisted of 19 persons who were normal on renal function test and did not show any abnormality of the kidney. Renal cortical and parenchymal thicknesses were measured at renal hilum level perpendicular to the renal surface by electronic caliper on contrast-enhanced transverse scan demonstrating the cortical nephrogram phase. Using student's test, the difference in renal parenchymal and cortical thickness between the two groups was tested for statistical significance. RESULTS: There was no significant difference in renal parenchymal thickness between the two groups(P>0.05) ; the patient group had a thicker renal cortex than the normal control group however (P<0.05). The ratio of renal cortical thickness to parenchymal thickness in early diabetic nephropathy patients(Rt.:0.041±0.051, Lt.:0.382±0.053) was significantly higher than in the normal control group (Rt.:0.331±0.067, Lt.:0.323±0.064). CONCLUSION: The kidney of early diabetic nephropathy patients had a thicker renal cortex than normal kidney.