An 11 year old Arabian gelding presented to Cornell’s Equine and Farm Animal Hospital emergency service with a history of intermittent unilateral epistaxis starting 3 months prior. Findings on initial examination and rhinoscopy were consistent with the presence of a progressive ethmoid hematoma. Radiography and CT were performed to determine the extent of the lesion. Due to the size and extent of the mass, it was decided to surgically remove it via a frontonasal flap. The mass was debulked and sent for histopathology, which confirmed the diagnosis of ethmoid hematoma. Progressive ethmoid hematomas are encapsulated, slow-growing, organized hematomas that arise from the ethmoid region in the horse. This paper will discuss the diagnosis, treatment, and pathogenesis of ethmoid hematomas in the horse.