Purpose: This study investigated the effect of coronal preparation by high-speed handpiece on the retention of cemented cast posts and cores. Materials and Methods: Cast posts and cores were fabricated for 90 extracted single-rooted human teeth cemented with zincphosphate cement and randomly divided into six groups of 15 specimens each. The six groups were matched randomly two by two, such that one of each of the matched groups was subjected to a 4-minute period of high-speed preparation of the cores. Castings from the first pair (1 and 2) were subjected to an axially directed removal force using a universal testing machine 15 minutes from the start of cement mixing; castings from the second (3 and 4) and third (5 and 6) pairs were tested at 1 hour and 24 hours, respectively, having been stored in water at 37°C for the waiting periods. The forces required for dislodgment of posts from their prepared spaces were recorded. Data were statistically analyzed using two- and one-way ANOVA and the Student's t test. Results: The results showed increased mean retentive strengths of posts as the time to testing increased for both unprepared and prepared groups. Significantly higher mean retentive strengths of posts were recorded for unprepared compared to prepared groups tested at 15 minutes and 1 hour after cementation. Conclusion: High-speed preparation had a significant negative effect on the retentive strengths of posts tested at 15 minutes and 1 hour after cementation, but not on those tested at 24 hours.