We completed a retrospective study of 270 patients with essential trigeminal neuralgia treated by gamma knife surgery. The target was localized on the retro-Gasserian portion of the nerve with 90 Gy at maximum. Among them, 150 patients were followed up more than 2 years. They were divided into 2 groups: pre-APS (41 patients) and post-APS (109 patients) treated by model C-APS since 2003. In the post-APS group, initial electric discharge was observed in 98.2% and at the last follow-up of at least 2 years in 79.8%. Complete recurrence was observed in 4.7% and postoperative complications were observed in 29.4%. These results were much better than those of the pre-APS group. There is no doubt that precise dose planning, C-APS treatment, so-called 'robotized micro radiosurgery', is important for improved treatment results.