Abstract Objective: To examine fecundability trends among sperm donors. Design: Retrospective analysis. Setting: University-based sperm bank and donor insemination program. Patient(s): Sperm donors and recipients. Intervention(s): A group of recipients underwent IUI with cryopreserved donor sperm. Fecundability was calculated for 20 sperm donors over 800 insemination cycles. Main Outcome Measure(s): Average fecundability per donor was compared for the first 40 cycles of a donor’s use and for those donors within a group of more fertile recipients. Sperm parameters, recipient ages, and number of unique recipients for each donor were analyzed. Result(s): Average donor fecundability is constant; however, individual donors demonstrated differences among their fecundabilities (overall mean, 0.09; range, 0.01–0.26). These differences persisted for donors among a group of more fertile recipients (overall mean, 0.12; range, 0.02–0.35). A donor’s fecundability at 15 cycles is predictive of his future performance. Conclusion(s): Differences in fecundability exist among sperm donors which cannot be discerned through routine semen parameters. Sperm donor fecundability should be analyzed periodically, and directors of sperm banks should consider discontinuing use of a donor whose outcome is substandard.