BACKGROUND: Epistaxis is very common during childhood. It occurs primarily in boys and is usually self-limiting. Trauma and nose picking are among the most common causes. In general, epistaxis can be easily treated with anterior nasal packing or electrocoagulation. METHODS: We report a case of an 8-year-old girl with severe unilateral epistaxis. RESULTS: The bleeding originated from a kaposiform hemangioendothelioma arising in the left nasal cavity and ethmoid sinus. The feeding vessels originating from the maxillary artery were first embolized. The tumor was then surgically removed through a combined external ethmoidectomy and endonasal approach. The postoperative course was uneventful. MRI at 6 months after surgery showed no tumor recurrence. CONCLUSIONS: We report a previously undescribed cause of epistaxis in children, namely, a kaposiform hemangioendothelioma. To our knowledge, this is the first such case in the English-language literature. The differential diagnosis of severe unilateral nasal bleeding among the pediatric population should include the possibility of a kaposiform hemangioendothelioma.