Purpose Masses involving the medial canthus and lacrimal sac fossa include dacryocystoceles and, less commonly, mucoceles, hemangiomas, diverticula, and lacrimal sac neoplasms. To our knowledge, juvenile xanthogranuloma presenting as a lacrimal sac fossa mass has not been previously reported. Methods We examined a 2-year-old boy who had epiphora in the left eye since birth and a mass in the left lacrimal sac fossa for 6 weeks. During surgery, left lacrimal probing disclosed obstruction at the level of the common canaliculus and lacrimal sac. Exploration and excision of the mass were performed. Results Histopathologic evaluation disclosed a juvenile xanthogranuloma characterized by an inflammatory cell infiltrate with foamy histiocytes and scattered Touton-type multinucleated giant cells. Conclusion Juvenile xanthogranuloma should be included in the differential diagnosis of a medial canthal and lacrimal sac fossa mass.