We report a case of respiratory epithelial adenomatoid hamartoma of the left maxillary sinus that initially presented as a periapical radiolucency involving the left maxillary first molar. Respiratory epithelial adenomatoid hamartoma is a rare lesion that occurs in the nasal cavity, paranasal sinuses, and nasopharynx. Most cases are found in the nasal cavity associated with the posterior nasal septum. Involvement of the maxillary sinus is very unusual, and only one other report of a respiratory epithelial adenomatoid hamartoma involving the maxillary antrum was found in a search of the literature. The current case is additionally unique as it was initially detected in the course of a dental examination. Awareness of this lesion is important because inverted schneiderian papilloma and adenocarcinoma may be included in the histopathological differential diagnosis. Conservative surgical removal is curative and recurrence has not been reported.