The treatment of hypertrophy of the masseter and temporal muscles has to date been dominated by conservative and surgical measures. Local therapy with type A botulinum toxin permits an alternative method of treatment. After targeted, sometimes electromyographically controlled, intramuscular injection of the affected muscles, marked inactivity atrophy occurred in the muscles of seven patients over the course of 3 to 8 weeks. This atrophy remained constant over a follow-up period of up to 25 months, and no side effects were observed. Because of its minimal invasiveness, this technique seems to have an advantage over conventional surgical therapy. Consequently, treatment with type A botulinum toxin can be regarded as a sensible alternative to surgery in cases of hypertrophy of the masseter and/or temporal muscles.