Trigeminal neuralgia is common painful disorder in pain medicine clinics. Gasserian ganglion radiofrequency thermocoagulation is one of the treatment option in patients with trigeminal neuralgia in refractory cases. The most commonly involved branch in trigeminal neuralgia is the mandibular branch. Masseter muscle is innervated by mandibulary nerve branch of the trigeminal nerve. The radiofrequency thermocoagulation therapy is used to ablate the affected trigeminal nerve branch and some of patients complain of subjective masseter weakness after this procedure. In theoretical basis, muscles innervated by target nerve are affected from ablation procedure. In this study the primary aim is to evaluate the change of the masseter muscle thickness in patients treated by gasserian ganglion radiofrequency thermocoagulation. The results may also show possible functional effect of the procedure related with masseter muscle.