Oscar is a 9 year old male castrated Golden Retriever Dog who presented for an oral mass located between the left mandibular premolar 3 and premolar 4, which was previously diagnosed by the rDVM as an acanthomatous epulis. Physical examinations did not find any major abnormalities other than the oral mass. Oral masses in dogs are most commonly squamous cell carcinoma, melanoma, or fibrosarcoma but also include chondrosarcoma, osteosarcoma, and the epulides. Original incisional biopsy reported chondrosarcoma, although later surgical biopsy revealed a chondroblastic osteosarcoma. Dental radiographs and CT scan revealed a large aggressive tumor causing boney lysis of the mandible. A mandibulectomy was performed. This paper discusses intraoperative and postoperative complications associated with mandibulectomy. The major intraoperative complication is hemorrhage from the mandibular artery. Postoperative complications include ranula formation, short term anorexia, dehiscence, instability of the remaining mandibles, and palatal contact ulceration resulting from the mandibular canine tooth after medial mandibular drift.