In case of failure of initial root canal therapy, modern endodontics provides clinicians with different treatment options to save the natural tooth from extraction. This article reviews the reasons for conventional treatment failure and discusses guidelines and diagnostic criteria for conventional and surgical re-treatment. The decision-making process for choosing among conventional re-treatment, surgical microendodontics, or extraction of the tooth with subsequent placement of an endosseous implant is described, and indications are illustrated by case examples.