A 17-year-old Paint gelding was presented with an 11 month history of unlateral mucopurulent nasal discharge. The patient had been treated 7 months earlier with maxillary check tooth repulsion of teeth 109 and 110 based on radiographic diagnosis of apical infections of those teeth. The nasal discharge persisted following that surgery until presentation to Cornell University Equine and Farm Animal Hospital. Upon presentation, sedated oral exam revealed a deep defect in the space created by repulsion of tooth 110. A dental probe could be passed several centimeters through this defect into the maxillary sinus. Radiographs revealed soft tissue opacification throughout the rostral maxillary and ventral conchal sinus. Sinusitis secondary to an extraction-related oromaxillary fistula was diagnosed. A standing maxillary flap sinusotomy was performed for debridement and lavage of the sinus. The oromaxillary fistual was curetted and packed at the oral aspect. Oromaxillary fistula formation is a relatively common complication of maxillary check teeth repulsion. This case report will discuss the diagnosis, treatment, and pathogenesis of oromaxillary fistula formation.