An 8-year-old Thoroughbred gelding presented for evaluation and investigation for recurrent unilateral epistaxis. Computer tomography (CT) confirmed the presence of an invasive and expansive progressive ethmoid hematoma (PEH) located in the right paranasal sinuses. The mass invaded the right paranasal sinuses compartments causing moderate leftward displacement of the nasal septum with subsequent collapse of the left nasal passages, complete obliteration of the right ethmoid turbinate, right infraorbital canal, and nasolacrimal duct. Also, impingement of the axial margin of the right orbit. A large frontonasal maxillary bone flap was performed standing under sedation and local anesthesia and the PEH was removed successfully with minimal surgical complications. The gelding made an unremarkable recovery from surgery and progressed well after recovering from post operative pleuropneumonia. Follow-up (25 months post operative) confirmed the reoccurrence of the PEH, but the horse remained healthy in pasture turn out.