This textbook attempts to describe in detail endodontic mishaps or procedural accidents that occur during access cavity preparation. First and foremost, an accurate diagnosis is essential for success of any treatment. Even after adopting a correct regimen, mishaps may occur, which have been classified into five broad categories: treating the wrong tooth, missed canals, damage to existing restoration, perforations and crown fractures. For treatment of the correct tooth, an accurate diagnosis along with marking the tooth prior to treatment is essential. A misdirected access opening might make it difficult for the dentist to identify all the root canals. Moreover, the decision for damaging an existing restoration, whether to remove indirect crowns or large restorations and which burs to penetrate various restorative materials, has also been mentioned. Also, perforations may occur which may be treated surgically or non-surgically. Lastly, crown fractures may result due to excessive tooth structure loss due to caries, access opening, etc. Thus, any treatment option should be considered, only after evaluating the long term prospects in maintaining the structural integrity of the tooth.