Endodontics is a complex branch of dentistry and clinician may encounter many unforeseen circumstances that may complicate his treatment. Such circumstances are called mishaps during endodontic procedures. These mishaps in endodontic therapy can be divided into mishaps occurring during the preparation of the access cavity, mishaps during root canal instrumentation and obturation. But others accidents can also happen, such as post space perforation during preparation for intracanal upgrade, irrigant related mishaps, tissue emphysema and instrument aspiration or ingestion. Regardless of the possibility that such mishaps can happen, clinicians should not be discouraged to approach endodontic therapy. If a clinician is well educated and diagnosis is properly set, most of the problems can be avoided. In case the mishap still occurs despite the experience and intuition of the therapist, his task is to recognize the mishap and to assess the ability of successful endodontic retreatment of a particular tooth. Therapy options for endodontic mishaps are non-surgical retreatment or endodontic surgery. Non-surgical retreatment is the first treatment of choice for the endodontic mishaps. In case of failure of non-surgical therapy or the presence of persistent periapical lesion, apical surgery or amputation or hemisection of the root is required. In this graduate thesis, except from the literature review, there are described three cases of endodontic mishaps and their treatment. First case shows midroot perforation of the buccal wall and it's treatment by filling real and iatrogenic root canal. Second case shows separated instrument in the cervical third of the tooth and it's removal from the root canal. Third case shows vertical fracture of the mesial root of mandibular molar and it's managment by doing hemisection of the mesial root. By knowing well the morphology of the pulp space, rules and techniques of the instrumentation and filling of the root canals, we can reduce the possibility of endodontic mishaps and increase success of endodontic treatment.