PURPOSE: The purpose of this study was to compare the in-vivo efficiency of vascular occlusion on radiofrequency ablation (RFA) lesion size in a rabbit kidney model. MATERIALS AND METHODS: RFA lesions were created in a single kidney in 20 rabbits using an internally cooled electrode. Twenty ablation zones (1 per kidney) were created using 4 different regimens: RFA without vascular occlusion (n = 5), RFA with renal artery occlusion (n = 5), RFA with renal vein occlusion (n = 5), RFA with renal artery and vein occlusion (n = 5). Seven days later, the rabbits were sacrificed and the lesions were excised. These groups were then compared with respect to the dimensions of the ablation zones and the changes in impedance and current during RFA. RESULTS: The maximum ablation zone width was the greatest in the renal artery and vein occlusion group (21.0+/-1.4 mm), followed by the renal artery occlusion group (17.8+/-1.0 mm), the renal vein occlusion group (17.4+/-1.1 mm), and the nonocclusion group (7.8+/-2.4 mm) (p < 0.05). No significant differences were observed for impedances and currents between the 4 groups. CONCLUSION: Vascular occlusion combined with RFA effectively increased ablation zone dimensions compared with RFA alone, and the best effect was accomplished by combined renal artery and vein occlusion.