BACKGROUND: To minimize the side effects of radiofrequency trigeminal rhizotomy by making a more selective minimal lesion for the target division of a trigeminal rootlet, we performed this study to evaluate the effectiveness and the selectivity of radiofrequency trigeminal rhizotomy using a 2 mm active tip electrode as compared to a 5 mm active tip electrode. METHODS: The authors evaluated 36 cases, in which radiofrequency thermocoagulation of a trigeminal rootlet was performed using a 2 mm active tip electrode or a 5 mm active tip electrode at 75oC for 60 seconds in patients suffering from trigeminal neuralgia. One month after each operation, we assessed the clinical effects, selectivity, and the side effects of these operations. RESULTS: Of the 36 patients, 34 patients experienced loss of tic pain. In terms of effectiveness, no difference was found between the two groups. In terms of selectivity, some superiority was shown by the 2 mm active tip electrode, but this was not statistically significant. Masseter weakness or dysesthesia occurred in six patients who suffered from tic pain in the V3 region, and who were operated upon with a 5 mm active tip electrode. Major complications like anesthesia dolorosa, and corneal anesthesia were absent in any patients. CONCLUSIONS: For target specific lesion generation of trigeminal rootlets, single lesion generation using a 2 mm active tip electrode may be as clinically effective as a 5 mm tip and is more selective in use.