Introduction Striking enlargement of the masseter muscles is common, scarcely a busy day passing in which a careful observer may not see at least one case of idiopathic masseter hypertrophy. Yet only 43 instances of this condition have been reported in some 20 articles * (excluding our own), which give the impression of dealing with a clinical rarity. Although various etiologic theories have been offered, the true nature of the condition remains obscure. Studies thus far employed —without yielding generally accepted evidence for any theory—include physical and neurological examination, x-ray study of the mandible, electromyography of the masseter and related muscles, surgical exploration with either biopsy or substantial muscle resection, and pathologic examination. As a surgical curiosity the condition might seem scarcely worthy of an extensive investigation. We believe, however, that it is of extraordinary psychosomatic interest. While casual references are made to psychic disturbances in eight of the reported cases,