Objective: To assess the influence of post-and-core systems on the resistance to fracture of mandibular premolars restored with metal crowns and a 2.0-mm cervical ferrule. Method and Materials: Forty extracted premolars were selected and divided into 4 groups of 10 teeth each. Samples were sectioned 2.0 mm coronal to the CEJ. Following canal preparation, four restorative treatments were performed: group 1, post and core cast in type IV gold alloy; group 2, prefabricated titanium post with composite resin core; group 3, prefabricated quartz-fiber post combined with composite resin core; and group 4, composite resin core without post. Posts (groups 1, 2, and 3) were cemented with resin cement. Metal crowns were fabricated using nickel-chromium alloy. Specimens were placed in acrylic resin blocks and filled up to 2.0 mm apical to the CEJ. Fracture resistance was assessed by applying a continuous compressive force on the buccal cusp of the crowns at a 45-degree angle until fracture. Results were analyzed using ANOVA and Tukey multiple comparison test at a significance level of 5%. Results: Mean loads at fracture were as follows: group 1 = 1,189.23 N, group 2 = 1,816.43 N, group 3 = 1,224.51 N, and group 4 = 2,010.63 N. Groups 2 and 4 presented statistically similar results; the same was observed in groups 1 and 3. However, groups 2 and 4 presented significantly better results than groups 1 and 3. Conclusion: Restoration of mandibular premolars with composite resin core (without post) showed an increased resistance to fracture when compared with other post-and-core systems whenever a minimum of 2.0 mm of remaining tooth structure was covered with a full metal crown (ferrule effect). Preservation of tooth structure was the most important factor in tooth resistance. Keywords: composite resin core, endodontically treated teeth, ferrule, post and core