OBJECTIVE. This study determined the effect of vascular occlusion on radiofrequency lesion shape, volume, and temperature in a porcine liver model. SUBJECTS AND METHODS. Radiofrequency lesions (n = 33) were created in the livers of six domestic pigs in vivo using a multiprong radiofrequency electrode. Lesions were randomly assigned to one of four vascular occlusion groups: portal vein, hepatic artery, Pringle maneuver (both hepatic artery and portal vein), or no occlusion. Radiofrequency parameters were time, 7 min; power, 50 W; and target temperature, 100°C. Temperatures were measured 5, 10, and 15 mm from the electrode. After the animals were sacrificed, the lesions were excised. Lesion volume, diameter, and shape; maximum temperature; and time exposed to lethal temperatures (42-60°C) were determined. RESULTS. Lesion volume was greatest with the Pringle maneuver lesions (12.6 ± 4.8 cm3), followed by occlusion of the portal vein (8.6 ± 3.8 cm3), occlusion of the hepatic artery (7.6 ± 2.9 cm3), and no occlusion (4.3 ± 1.0 cm3) (p < 0.05). Maximum lesion diameter was similar with the Pringle maneuver (3.3 ± 0.3 cm), the portal vein (3.3 ± 0.2 cm), and the hepatic artery (3.2 ± 0.2 cm) groups compared with no occlusion (2.6 ± 1.0 cm) (p < 0.05). Minimum lesion diameter ranged from 2.9 cm for Pringle maneuver lesions to 1.0 cm for lesions with no occlusion (p < 0.05). Vascular occlusion increased the time tissue was exposed to lethal temperatures (>42-60°C) and created more spherical lesions than no occlusion. CONCLUSION. Vascular occlusion combined with radiofrequency ablation increases the volume of necrosis, creates a more spherical lesion, and increases the time tissue is exposed to lethal temperatures when compared with radiofrequency alone. Most of this vascular occlusion effect could be accomplished with hepatic artery occlusion alone.