A woman in her 30s presented with a 3-month history of painful swelling of the left hard palate and cheek. The growth also caused malocclusion and ipsilateral upper lip numbness. She reported no recent trauma; no difficulty speaking, breathing, or swallowing; no epistaxis, nasal congestion or nasal drainage; and no recent fevers. She did have a history of recent pericoronitis, but several courses of antibiotics were unhelpful. Physical examination revealed a submucosal growth centered on the mesial aspect of the left maxillary alveolus. Transnasal endoscopy was unremarkable. Contrasted computed tomographic and magnetic resonance imaging showed a heterogeneously ossified lesion filling the left maxillary sinus, with local destruction of hard palate and alveolar bone (Figure, A and B). Positron emission tomographic scans highlighted the fluorodeoxyglucose-avid nature of both the tumor and associated cervical lymphadenopathy. A biopsy showed a tumor with lobular architecture, an incomplete peripheral ossified rim (Figure, C), and focal areas of osteoid matrix. Higher power showed atypical cells with increased mitotic activity in a myxoid stroma (Figure, D). Immunostains were negative for S100, pankeratin AE1/AE3, SMSA, and GFAP.