A sinonasal mucocele can develop after the obstruction of a sinus ostium, which can occur secondary to trauma, infection, a neoplasm, or an iatrogenic cause. These mucoceles typically arise in the frontal and ethmoid sinuses. Sinonasal mucoceles are epithelium-lined cysts that can gradually expand to fill a paranasal sinus. They can present with ophthalmologic, rhinologic, and neurologic symptoms. There are reports in the literature of sinonasal mucocele development after radiation for nasopharyngeal carcinoma. However, these cases are rare; when they do occur, they tend to arise in the sphenoid sinus. We describe the case of a 21-year-old man who had undergone external-beam radiotherapy for a right maxillary sinus rhabdomyosarcoma at the age of 4 years and who subsequently developed bilateral maxillary sinus mucoceles and multiple other known complications of radiation therapy. To the best of our knowledge, this is the first case of postirradiation bilateral maxillary sinus mucoceles to be reported in the literature.