Choanal polyps arise from inflamed, edematous mucosa in the paranasal sinuses. They extend into the choana and cause nasal obstruction and mouth breathing. In most cases, these polyps arise in the maxillary sinus, but rare cases of origin in the sphenoid sinus and other nasal structures have been reported. The presence of a choanal polyp in an atypical location can lead to diagnostic confusion and exploration of the wrong sinus at surgery. The author reports the case of a 15-year-old girl who was diagnosed with a sphenochoanal polyp. The patient was successfully treated via an endoscopic surgical approach.