Significant advances in the field of surgical endodontics have resulted in more predictable outcomes. A thorough understanding of the etiology of posttreatment endodontic disease will serve as a basis for better surgical treatment. Technically, EMS allows surgeons to have better opportunities to identify and eliminate the etiologies as compared to TES. In this chapter, the variations in outcomes between EMS and TES observed in the literature were identified by contrasting the differences in surgical techniques. A striking difference in success rates between the two surgical treatment modalities exists, and it is explained by the different techniques employed in achieving disinfection and attaining an adequate apical seal. Finally, the results of various outcome studies should be carefully interpreted with a full understanding of prognostic factors, because the hidden heterogeneity in different studies can alter the outcomes significantly.