Perhaps the most frustrating scenario in dentistry lies in the apparently well-instrumented and well-obturated tooth that, becomes symptomatic after treatment of shows a periapical lesion on recall examination. Conventional root canal treatment demands stringent adherence to asepsis, awareness of canal morphology, and mastery of a variety of clinical techniques. But the risk of endodontic failure does not end with canal obturation. The quality of the coronal restoration may have a greater bearing on the ultimate success of a case than the quality of the root canal treatment itself. This review of the endodontic literature will define coronal leakage, describe its influence on endodontic treatment failures, and make specific recommendations on prevention.