The formation of a new joint between a pathologically elongated coronoid process and the body of the malar homolateral bone is known as Jacob's disease. Coronoid process hyperplasia was first described in 1853 by Von Langenbeck, and it was not until 1899 when Oscar Jacob described the disease that it was named after him. Jacobs's disease is an uncommon entity with only a few documented cases in the literature. The condition first manifests with progressive limitation of mouth opening and facial asymmetry. Pain is uncommon and it mainly affects young patients. Different factors have been postulated as possible causes, including temporal muscle hyperactivity, previous trauma, chronic disc displacement of the ipsilateral temporomandibular joint, endocrine stimuli, and genetic alterations. Definitive diagnosis is by histopathology and it is necessary to confirm bone hyperplasia, the presence of cartilage and synovial capsule forming the new joint between the malar bone and the coronoid process. We report a 52-year-old woman patient with a history of childhood trauma in the right preauricular region. She came to our department with a 2-year history of progressive limitation of mouth opening. Computed tomography (CT) revealed a right coronoid process elongation, in contact with the homolateral malar bone, causing it to deform. Surgery with general anesthesia was performed using an intraoral vestibular approach. Histopathology confirmed the diagnoses of Jacob's disease. © Medicina Oral S. L.