Abstract: Objective: To investigate the cause of failure in all endodontically treated teeth that were evertually extracted.Methods: The clinical data of 121 extracted teeth which had previously received endodontic therapy were analysed.Results: Of the teeth, 61.2% were prosthetic failures which were due primarily to crown fracture.29.8% were periodontal failures. Only 9.0% of the failure were due to endodontic causes.Conclusions: Teeth that had been crowned have greater longevity than the uncrowned ones.The endodontic failure is rarelly seen,but once it occurs,the consequences are serious.