We sought to evaluate the response of 6 patients with masseter muscle hypertrophy to botulinum toxin type A therapy. Six patients with unilateral or bilateral masseter muscle hypertrophy received intramuscular injection of the botulinum toxin type A. The functional and cosmetic results were evaluated as well as recurrence. In all patients, satisfactory regression of the masseter muscle hypertrophy occurred and mild muscular pain was relieved. Recurrence was observed in 2 cases. The use of botulinum toxin type A in masseter muscle hypertrophy therapy was shown to be a successful and safe treatment method. This procedure to control parafunctional activities involving the masticatory muscles of patients appears to be useful.