Coronoid process enlargement may be unilateral or bilateral. Bilateral hyperplasia of the coronoid process of the mandible is defined as an abnormal elongation of the coronoid process, formed of histologically normal bone. The main clinical finding is a progressive, painless difficulty in opening the mouth, due to contact with the temporal surface of the zygomatic bone or medial surface of the zygomatic arch. The aetiology of the complaint is unknown, although several theories have been postulated, including hyperactivity of the temporal muscle, causing reactive elongation of the coronoid process, dysfunction of the temporomandibular joint caused by chronic disc displacement, which would be related with cases of unilateral hyperplasia and is mentioned as one of the causes of Jacob’s disease, endocrine stimuli, traumatism and even genetic and family factors.