The primary goal of endodontic treatment is to preserve the tooth as a functional unit. Although root canal therapy is mostly routine, certain mishaps and complications can occur due to unpredictable circumstances or insufficient caution of the clinician. This thesis aims to describe possible mishaps and complications during endodontic treatment, ways to prevent them, and if mishaps and complications do occur, the possibilities of their treatment and their influence on the outcome of therapy. Errors and complications of endodontic treatment can be classified into mishaps related to access cavity preparation, mishaps during root canal instrumentation, mishaps during root canal irrigation, and errors during root canal filling. Other mishaps include therapy of the wrong tooth, foreign body ingestion or aspiration, nerve paresthesia, inadequate coronary sealing, and mishaps related to preparation for intracanal posts. Above all, it is important to prevent potential mishaps, and if they do occur, to know how to recognize them, so that they can be treated appropriately and that their impact on the long­term survival of the tooth can be assessed. The first choice for dealing with mishaps is a non­surgical method, and if that is not sufficient, a surgical approach is required. By having good knowledge of the anatomy of the tooth and the morphology of the endodontic space, and by following all the rules of diagnosis and the treatment plan, most mishaps and complications can be avoided, thereby increasing the probability of a positive outcome and success of endodontic treatment.