Introduction: Long-term predictability of restored endodontically treated teeth is important for the decision of tooth retention versus extraction and implant placement. The purpose of this study was to validate the hypothesis that preoperative factors can predict the long-term prognosis of molars requiring endodontic and restorative treatment for future prognostic investigations., Methods: A clinical database was searched for molar endodontic treatments with crown placement and a minimum of 4-year follow-up. Charts of 42 patients with 50 individual treatments were randomly selected. Information concerning crown lengthening; periodontal diagnosis; attachment loss; furcation involvement; mobility; and internal, external, or periradicular resorption was recorded. Radiographs from treatment initiation and follow-up were digitalized. The presence of apical periodontitis was evaluated. Available ferrule was calculated from bitewing radiographs using CAD software (AutoCAD; Autodesk, Cupertino, CA). The resulting data, age, sex, and times of restoration and follow-up were analyzed for correlation with the presence of apical radiolucency at follow-up and the following four possible outcome scenarios: "no event," "nonsurgical retreatment," "surgical retreatment," or "extraction" using Spearman rank order correlation analysis., Results: Patients' ages ranged from 19 to 87 years, 22 were male and 20 female, and 48 teeth (96.0%) were retained at follow-up. Of those, 44 (88.0%) were without intervention ("no event"), and four (8.0%) underwent surgical or nonsurgical retreatment. Two teeth (4.0%) had been extracted. Significant positive correlations existed between "untoward events" (any form of retreatment or extraction) and "prognostic value according to periodontal status" (p = 0.047) and "attachment loss" (p = 0.042)., Conclusion: The only preoperative factors significant for the prognosis of restored endodontically treated molars were related to periodontal prognostic value and attachment loss. It can be concluded that it may be difficult to predict the prognosis of molars in need for endodontic treatment and restoration from prognostic factors not related to periodontal disease., (Copyright © 2011 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.)