Purpose. To evaluate the risk of radiofrequency ablation treatment failure for hepatocellular carcinomas (HCC) next to large vessels. Materials and methods. Between May 2000 and October 2002, from a total of 83 patients treated by radiofrequency ablation for HCC in a single center, 13 patients with tumor <= 3.5 cm contacting a vessel >= 3 mm in diameter (Group A) were matched with 13 patients with similar size tumors located away from large vessels (Group B). Immediate response and recurrence rate were evaluated on CT. Results. After mean follow-up interval of 39 +/- 16.5 months for Group A and 39 14 months for Group B, local recurrence rates were 7/12 versus 1/12 respectively (p=0.03). For Group A, 6/7 local recurrences clearly contacted a large vessel. Conclusion. The cooling effect from flowing blood in large vessels markedly increases the rate of local failure of radiofrequency ablation for small HCC located near large vessels.