An 18-year-old Dutch man presented himself at the emergency department of a hospital, with a spontaneously arisen unilateral swelling at the mandibular angle during occlusion. No additional complaints were present and the patient had no previous experience of such swelling. After an assessment of the patient's history and diagnostic procedures, the swelling was diagnosed as a partial rupture of the masseter muscle fascia. On the basis hereof a conservative approach was selected, and the swelling subsequently disappeared.