Renal length, height, width, resistive index (RI), size of cortex, and medulla were determined by renal ultrasonography in 50 healthy Korean domestic short-hair cats. In the sagittal plane, the renal length was 3.83 +/- 0.51 cm (mean +/- SD) in the left kidney and 3.96 +/- 0.48 cm in the right kidney, whereas the renal height was 2.42 plusmn; 0.27 cm in the left kidney and 2.36 plusmn; 0.28 cm in the right kidney. In the transverse plane, the renal height was 2.42 +/- 0.28 cm in the left kidney and 2.38 +/- 0.27 cm in the right kidney, whereas the renal width was: 2.65 +/- 0.35 cm in the left kidney and 2.63 +/- 0.31 cm in the right kidney. In the dorsal plane, the renal length was 3.84 +/- 0.53 cm in the left kidney and 3.97 +/- 0.54 cm in the right kidney, whereas the renal width was 2.65 +/- 0.34 cm in the left kidney and 2.66 +/- 0.33 cm in the right kidney. There were no significant differences (p > 0.05) among the same structure sizes measured in different planes. In the sagittal plane, the size of the renal cortex was 0.47 +/-; 0.08 cm in the left kidney and 0.47 +/- 0.08 cm in the right kidney, whereas of the size of the renal medulla was 0.55 +/- 0.30 cm in the left kidney and 0.50 +/- 0.07 cm in the right kidney. RI evaluated by pulsed wave Doppler sonography was 0.52 +/- 0.05 in the left kidney and 0.55 +/- 0.05 in the right kidney. The actual renal dimensions determined by gross examination were not statistically different from those determined by ultrasonography. Furthermore the renal dimensions and RI were statistically correlated to the body weight of cats.