This report describes the 5-year clinical and radiographic follow-up of an accidental extrusion of a root canal filling material into the maxillary sinus and emphasizes the importance of monitoring of similar cases. The most favorable prognosis is achieved by surgically removing the extruded material from the sinus. Excess zinc oxide-eugenol-based materials in the sinus might cause aspergillosis sinusitis, and this entity often needs many years to develop. In this case, endomethasone was the filling material; however, the patient refused to undergo any surgical intervention. After a follow-up period of 5 years, the patient had no symptoms and radiographic examination disclosed no pathologic changes in the antrum.