PURPOSE: To evaluate Doppler sonographic findings of acute renal vein thrombosis in rabbit model induced by renal vein ligation, with an emphasis on the changes in resistive index (RI) on serial follow-up. MATERIALS AND METHODS: Conventional and Doppler sonographies were performed immediately after ligation and 24, 48, and 72 hours after ligation in 12 rabbits weighing 4.5-5.0 kg. We focused on changes in kidney size and echogenicity with conventional sonography and resistive index by time interval and Doppler waveforms with Doppler sonography. RESULTS: Kidney size increased markedly immediately after ligation, and increased slowly until 48 hours after ligation with no change observed afterwards. Echogenicity increased both in the renal cortex and the medulla. RI increased remarkably to an average of 1.38 immediately after ligation, and increased to a peak average of 1.64 48 hours after ligation. After 72 hours RI decreased slightly to 1.59. Reverse 'plateau-like' diastolic waveform was seen in 27 trials (56%) on follow up Doppler sonograms. CONCLUSION: The increase in RI was thought to be due to the increase in renal arterial vascular resistance caused by venous outflow obstruction. The decrease in RI with time suggested adaptation of intrarenal circulation to renal vascular change. Also, the reverse 'plateau-like' diastolic waveform was the predominant waveform.