This study describes 6 cases of endodontic overfilling with successful clinical outcomes during long-term (up to 35 years) radiographic follow-up. Successful endodontic treatment depends on proper shaping, disinfection, and obturation of root canals. Filling materials should completely fill the root canal space without exceeding the anatomical apex. Overfilling may occur when the filling material extrudes into the periapical tissues beyond the apex. The present case series describes 6 root canal treatments in which overfilling of root canal sealer and gutta-percha accidentally occurred. Patients' teeth were periodically checked with periapical radiographs in order to evaluate the outcomes during long-term follow-up. All cases showed healing and progressive resorption of the extruded materials in the periapex. The present cases showed that if a 3-dimensional seal was present at the apical level, overfilling did not negatively affect the long-term outcomes of root canal treatment.