The key factors that help to save a pulpally involved tooth in the dental arch are the the accurate diagnosis, prevention, and treatment of diseases of pulp. However, the root canal system anatomy plays a remarkable role in endodontic success and failure. Other factors such as instrumentation technique, proper mechanical debridement, obturating materials and techniques, irrigants, root canal morphology, root resorption, coronal leakage and follow up period also play an important role for the success of the treatment. Sometimes, despite an ideal root canal treatment, failures do occur. This paper reviews the endodontic failures and the factors associated with it in order to help in increasing the chances of preventing the possible endodontic treatment failures.