We report the clinicopathologic features of 31 cases of respiratory epithelial adenomatoid hamartomas occurring in the nasal cavity, paranasal sinuses, and nasopharynx. The patients included 27 men and 4 women ranging in age from 27 to 81 years (median, 58 years). Symptoms included nasal obstruction, nasal stuffiness, deviated septum, epistaxis, and chronic (recurrent) rhinosinusitis. The symptoms occurred over various time periods from as short as a few months to up to 8 years in duration. Physical examination identified the presence of a polypoid mass lesion(s), most often identified in one or both nasal cavities (n = 22). Within the nasal cavity the most common site of occurrence was the nasal septum, particularly along its posterior aspect. Other areas within the nasal cavity were also involved, as were the ethmoid sinus, frontal sinus, and nasopharynx. The gross appearance of the mass lesions suggested a diagnosis of an inflammatory polyp, but because of subtle differences, including frequent occurrence along the nasal septum and a more indurated quality, these polyps were considered unusual for the typical inflammatory polyps. Histologically, these lesions were characterized by a prominent glandular proliferation lined by ciliated respiratory epithelium originating from the surface epithelium. The differential diagnosis of these adenomatoid hamartomas includes schneiderian papillomas of the inverted type and adenocarcinomas. Diagnostic misinterpretations may result in untoward surgical intervention. Limited but complete surgical resection was the treatment of choice, following which there were no instances of recurrent disease.