Radiofrequency ablation (RFA) has been reported to be a minimally invasive and effective procedure for the treatment of hepatocellular carcinoma (HCC). However, the pattern of recurrence and complications following RFA have yet to be fully identified. During the period January 2000 to December 2006, we performed HCC resections in 15 patients who developed local recurrence after RFA, as well as in 144 patients without RFA. In patients with local recurrence of HCC after RFA, the tumors showed a more invasive growth, more vascular invasion and less differentiation compared with tumors of patients without RFA. In 6 of the 15 patients with recurrence after RFA, needle biopsy of the HCC was performed before tumor ablation. In five of these 6 patients, dedifferentiation of the tumor was observed. These findings suggest that heat shock due to RFA induces dedifferentiation of HCC. Recurrence after RFA may result in an aggressive tumor that precludes any possibility of cure. RFA must not be considered a suitable alternative to surgery in patients with a low surgical risk. Instead, RFA should be performed according to strict indications by skilled operators using the latest devices.