PURPOSE: To assess the feasibility and safety of using a cooled-tip electrode to perform percutaneous radiofrequency ablation of kidney tissue in rabbits, and to evaluate the ability of CT to reveal the appearance and extent of tissue necrosis during follow-up after ablation. MATERIALS AND METHODS: Using ultrasound guidance, a 17-G, cooled-tip electrode was inserted into the right lower portion of the kidney in 26 New Zealand White rabbits. Radiofrequency was applied for 2 mins, and biphasic helical CT scanning was used to assess tissue destruction and the presence or absence of complications immediately after the procedure and at 24 hrs, 2 and 3 days, and 1, 2, 3, 4, 5, 6 and 7 weeks. The study had three phases: acute [immediately killed : N=10]; subacute [killed at 24 hrs (n=3), 2 days (n=3), 3 days (n=1) : N=7]; chronic [killed at 1 week (n=4), 2 weeks (n=2), 4 weeks (n=1), 7 weeks (n=1) : N=8]. After the animals were killed, their kidneys were histopathologically examined and the radiologic and pathologic findings of lesion size and configuration were correlated. RESULTS: In each instance, ultrasound-guided radiofrequency ablations of the lower pole of the kidney were technically successful. Contrast-enhanced biphasic helical CT revealed regions of hypoattenuation devoid of parenchymal enhancement, and these correlated closely with true pathologic lesion size (r=0.884; p>0.05). In subacute and chronic models, CT scanning revealed gradual spontaneous resorption of the ablated lesion and the presence of perilesional calcification. Histopathologically, in the acute phase the ablated lesions showed coagulative necrosis and infiltration of inflammatory cells, and in the chronic phase there was clear cut necrosis of glomeruli, tubules and renal interstitium, with diminishing inflammatory response and peripheral fibrotic tissue formation. CONCLUSION: Ultrasound-guided renal radiofrequency ablation is technically feasible and safe. In addition, the avascular lesion measured at contrast-enhanced helical CT closely correlated with the size of ablated tissue. Contrast-enhanced CT may therefore be used for serially monitoring the effect of radiofrequency ablation. In the future, RF ablation may offer an alternative treatment option for renal cancer.