Antrochoanal polyp is a benign, solitary polypoid lesion arising from the edematous mucosa of the maxillary sinus and extending through the maxillary ostium into the nose. In children, it constitutes 33% of all nasal polyps. It presents most commonly with unilateral nasal obstruction and purulent rhinorrhea. Surgery is the usual treatment for antrochoanal polyps. The primary aim of treatment for antrochoanal polyp must be complete removal with total cleaning of the maxillary sinus. In this article, we present a case of a 13-year-old boy with an antrochoanal polyp who complained of difficulty in breathing and swallowing; the differential diagnosis of nasopharyngeal masses and the treatment of antrochoanal polyps in children are also discussed. Antrochoanal polyps present most commonly with unilateral nasal obstruction; however, they sometimes present atypically. Clinical manifestations may mimic other neoplasms in the nasal cavity and nasopharynx. Nasopharyngeal masses must be evaluated by endoscopic examination and radiologic imaging before surgery to avoid unnecessary and harmful surgical techniques. Reporting this case is important to direct attention of the Ear, Nose and Throat specialist and pediatricians when facing similar cases.