Purpose: To evaluate the clinical performance of direct posterior composite restorations with and without short glass-fiber (SGF) reinforced composite in endodontically treated teeth. Materials and Methods: Twenty-four patients (mean age 32.5 years) were included in the study and two molars of each patient received endodontic treatment. After endodontic treatment, one tooth was restored with G-aenial Bond/fiber-reinforced composite (everX Posterior GC) using a microhybrid composite (G-aenial Posterior), and the other tooth was restored with G-aenial Bond/microhybrid composite (G-aenial Posterior). The modified USPHS criteria were used to evaluate the restorations at baseline, 1-, 2-, and 3-year follow-ups. Results: The success rate of the everX Posterior and G-aenial Posterior restorations after 3 years was 78.3% and 91.3%, respectively. Five everX Posterior restorations and two G-aenial Posterior restorations failed. Based on the criteria used in this study, no significant differences between the two restorations were found at any evaluation time. Conclusion: All restorations showed acceptable clinical performance regarding all evaluation criteria, apart from the failed restorations. The main cause of restoration failure was restoration fracture. The failure rate of everX Posterior restorations was higher than G-aenial Posterior restorations. Keywords: glass-fiber–reinforced composite, microhybrid composite, self-etching adhesive, direct posterior composite, endodontically treated teeth, clinical study, clinical performance