Gorham disease, or massive osteolysis, is a rare condition of unknown etiology. The disease is characterized by spontaneous progressive osteolysis of 1 or more skeletal bones. The mandible is the most commonly involved bone in the maxillofacial region. This article reports a case of Gorham disease with mandibular involvement in a 46-year-old male patient with a 7-year follow-up. In this case, we performed lower right mandibular osteotomy and reconstruction with a phased titanium plate. Postoperative follow-up showed continued mandibular bone loss that was progressing to the contralateral mandible. Massive osteolysis of the mandible is a rare clinical condition that must be differentiated from mandibularosteomyelitis, benign and malignant tumors, as well as hyperparathyroidism. Improved differential diagnoses and disease follow-up are required to effectively manage massive osteolysis.