This case report describes a seven year old mixed breed gelding that presented for evaluation of unilateral epistaxis. Upon physical examination, there was right-sided airflow obstruction and a hemorrhagic/mucoid nasal discharge with a fetid odor. Stertor and facial deformity were also obvious. Endoscopy of the upper airways revealed a dark mass with irregular borders filling the right nasal passage. Skull radiographs demonstrated increased opacity in the right nasal passage and conchofrontal sinus. Based on these results, a diagnosis of progressive ethmoidal hematoma (PEH) was suspected. Treatment consisted of surgical ablation of the lesion through a frontonasal bone flap. Histopathologic examination of the mass confirmed the diagnosis of PEH. This paper reviews the presentation, proposed pathogenesis, diagnosis, and prognosis of PEH using a case example. Alternative treatments are also detailed.