Close proximity between the maxillary teeth roots and the maxillary sinus can lead to an unintentional deposition of endodontic obturation materials into the latter. Among these materials the injectable thermoplasticized gutta-percha as a consequence of overfilling. In this report a case of extensive gutta-percha extruded into the maxillary sinus during root canal treatment on the 2nd upper left molar is presented.