Ectopic teeth are rarely found in the maxillary sinus. When they are, they represent an anomaly of odontogenic development that is generally associated with odontogenic cysts, trauma, or idiopathic etiology. Although affected patients are often asymptomatic, documented morbidities include sinus disease that is often refractory to treatment. The diagnosis is usually made by plain-film radiography. Computed tomography is indicated when an ectopic tooth is associated with an antral mass and prior to surgery. Treatment of symptomatic patients and those with an antral mass is surgical, with either a Caldwell-Luc operation or an endoscopic procedure. We describe what we believe is the first reported case of a third molar in the roof of the maxillary sinus associated with a mucocele, and we review the literature.