The authors present an 18-month-old female infant with congenital trismus. Computed tomography and magnetic resonance imaging were not helpful in determining the cause. A surgical endoscope was used to explore her temporomandibular joints and temporal fossae, thus avoiding the morbidity of a bicoronal incision. The cause was bilateral fibrous bands on the anterior border of the masseter muscles. Incision of these fibrous bands led to relief of the trismus. This finding is consistent with a previously described variant of the Hect-Beals-Wilson trismus-pseudocamptodactyly syndrome. This patient, however, had no evidence of the autosomal dominant inheritance pattern nor did she exhibit pseudocamptodactyly, both of which are generally ascribed to this syndrome. Unfortunately the trismus recurred 3 months postoperatively.