To try and explain the frequency of pathologic processes involving the masseter muscle.Anatomical and histological evaluation of the masseter muscle and its partial continuity with the medial pterygoid muscle. Retrospective evaluation of 21 cases of pathology of the masseter muscle imaged by CT and/or MRI.Two main groups of pathology are identified: benign masseter hypertrophy and hemodynamically inactive vascular malformations. Other etiologies are quite varied. Some are secondary to processes involving the nearby mandible and parotid gland. Others, including tumors, involved the masseter muscle in a non specific fashion. CT and especially MRI were quite valuable with accurate diagnosis in 17/21 cases, two of which with the help of clinical data.The main question regarding the preferential involvement of the masseter muscle over nearby muscles remains unanswered.