Introduction Mucoepidermoid carcinoma (MEC) is a tumor originated from the epitheliumof the glandular excretory ducts and has highly variable biological potential. It is the most prevalent cancer of the salivary glands. The present report aims to describe a case of nasal mucoepidermoid carcinoma that developed after adjuvant radiotherapy (RT) treatment of a recurrent pituitary macroadenoma. Case Report Male patient, 62 years old, presented with recurrent nasal epistaxis on the right, associated with intense pulsatile headache, visual analogical scale (VAS) 10/10, with improvement only with the use of opioids andmorphine. After undergoing oncological screening and study by imaging exams, the presence of an expansive seal lesion with suprasellar extension was seen, involving the medial wall of the cavernous segment of the right carotid artery and the anterior cerebral artery, as well as the presence of a new expansive lesion in the right nasal cavity, with ethmoid bone invasion superiorly and medial orbit wall invasion laterally, compressing the ipsilateral optic nerve canal. Discussion Sinonasal neoplasms represent a small portion of all malignancies of the upper aerodigestive tract, accounting for<5% of these neoplasms. The development of MEC involves risk factors such as occupational issues, history of trauma and surgery involving the nasal area, and radiation exposure, as in previous RT. Conclusion Mucoepidermoid carcinoma is an uncommon neoplasia and can be associated with RT treatment, as used in cases of recurrent pituitary macroadenoma. In general, surgical resection to obtain free margins of neoplastic tissue is the aimed treatment, seeking better prognosis.