This report describes the clinical presentation, diagnosis, treatment, and prognosis for a canine with maxillary osteonecrosis, as well as proposed etiologies of the disease process. The patient, an 11-year-old female spayed English springer spaniel, presented to the Cornell University Hospital for Animals’ Internal Medicine Service for evaluation of a three-month history of coughing. After ruling out various causes of a cough, sedated oral examination revealed a necrotic lesion caudal to the left maxillary first molar that was clinically diagnosed as maxillary osteonecrosis. Surgical treatment consisting of sequestrectomy and debridement was performed, followed by long-term targeted antibiotic therapy, antiseptic oral rinses, and pain management.