PURPOSE: Depth electrodes recordings may be required in some cases of epilepsy surgery to delineate the best region for cortical resection. We usually implant depth electrodes according to Talairach's stereoelectroencephalography (SEEG) method. By using these permanently implanted depth electrodes, we are able to perform radiofrequency (RF)-thermolesions of the epileptic foci. We report the technical data required to perform such multiple cortical thermolesions, as well as preliminary results in terms of seizure outcome in a group of 20 patients. METHODS: Lesions were performed by using 100- to 110-mA bipolar current (50 V), applied for 10 to 50 s. Each thermocoagulation produced a 5- to 7-mm diameter cortical lesion. In total, two to 16 lesions were performed in each of the 20 patients. Lesions were placed without anesthesia. No general or neurologic complication occurred during the procedures. Two transient postprocedure side effects, consisting of paresthetic sensations in the mouth and mild apraxia of the hand, were observed. RESULTS: At a follow-up time of 8 to 31 months (mean, 19 months), 15% of the patients became seizure free, 40% experienced a > or =80% reduction of their seizure frequency, and 45% were not significantly improved. CONCLUSIONS: SEEG-guided RF thermolesions is a safe technique. Our preliminary results indicate that such lesions can lead to a significant reduction of seizure frequency and could be proposed as a palliative procedure if no resective surgery is possible. A randomized controlled trial is needed to determine which patients are likely to respond to SEEG-guided RF thermolesions.