Introduction: Defects caused by root resorption are often associated with a variety of idiopathic, external resorptions or perforations located at the mid‐third of the root surface. These defects can lead to gingival inflammation, breakdown of periodontal fibers, bone resorption, and damage to the periodontal apparatus. Treatment protocols that preclude tooth extraction are important adjuncts toward an ultimate goal of tooth/root preservation. Although a number of materials have been proposed to repair root resorption defects, only a few have been effective in the long‐term management of subgingival defects.Case Presentation: This case report presents long‐term follow‐up of a subgingival, external root resorption lesion that was successfully treated with mineral trioxide aggregate (MTA) and a coronally advanced flap. At 30 months, the results revealed gain in clinical attachment, reduction in probing depth, additional bone formation, and, ultimately, preservation of the gingival margin and esthetic appearance of the tooth.Conclusion: The use of MTA appears to be a viable and effective material to treat subgingival root resorption defects while also preserving the function and esthetics of the natural dentition.