Objective: To compare in vitro the retentive values of stainless steel, parallel-sided posts to quartz-fiber, tapered posts for 2 different dowel lengths (5 and 10 mm). Method and Materials: Both post systems were cemented with a dual-cure adhesive resin cement. Single-rooted extracted human teeth (n = 40) were decoronated and randomly divided into 4 groups of 10 samples each. Posts of 5 and 10 mm in length were luted with the resin cement. Each sample was placed on a universal testing machine, and using a push-out method, a vertical load was applied at a crosshead speed of 2 mm/min. The amount of force required to dislodge the post was recorded. The effect of post type and length was evaluated using a 2-way analysis of variance. Results: A statistically significant main effect was found for post length (P .001), with the 10-mm posts of both post systems requiring greater force to dislodge than the 5-mm posts. There was no interaction between post length and post type (P > .05). Conclusion: It is concluded from this study that there is no statistical difference in retention between quartz-fiber, tapered posts and stainless steel, parallel-sided posts when they are cemented with the same resin cement (P > .05). The study also concludes that adequate retentive values are achieved with both post systems at the shorter, 5-mm post length. Palabras clave: post and core, post retention, quartz-fiber post, root canal therapy, stainless steel post