Purpose:This study evaluated the effect of cement, post material, surface treatment, and shape (1) on the retention of posts luted in the root canals of extracted human teeth and (2)on the failure morphology. Materials and Methods:Posts of titanium alloy (ParaPost XH), glass fiber (ParaPost Fiber White), and zirconia (Cerapost) received one of several surface treatments—sandblasting, CoJet treatment, application of Metalprimer II, or sandblasting followed by silane application—and were then luted in the prepared root canal of human incisors and canines (n = 10). Following water storage at 37°C for 7 days, retention was determined by extraction of the posts. Failure morphology of extracted posts was analyzed and quantified stereomicroscopically. Results:Type of luting cement, post material, and shape of post influenced the retention and failure morphology of the posts. Because of limited adherence of the cement to the root canal, surface treatments did not always have a positive effect on retention. Conclusion: Choice of luting cement was critical for all three types of posts. Parallel posts showed superior retention to tapered posts. Int J Prosthodont 2004;17:307–312.