OBJECTIVE: To determine the impact of a cryopreservation program on pregnancy rates and multiple-pregnancy rates in ART cycles. DESIGN: Retrospective study. SETTING: University teaching hospital. PATIENT(S): Women who underwent stimulation for in vitro fertilization at the Jones Institute for Reproductive Medicine between October 1987 and June 1999. INTERVENTION(S): Analysis of pregnancy and multiple-pregnancy rates based on the number of embryos transferred. MAIN OUTCOME MEASURE(S): Implantation; pregnancy and multiple-pregnancy rates. RESULT(S): Pregnancy rates per transfer increased from 9% when one embryo was transferred to 20% with two embryos, 35% with three embryos, 40% with four embryos, and 41% with five embryos. The rate of twin pregnancies increased to 21% with two embryos, 23% with three embryos, 21% with four embryos, and 22% with five embryos. The triplet pregnancy rates were 8% with three embryos, 9% with four embryos, and 2% with five embryos. A theoretical model limiting the number of embryos transferred to two with cryopreservation and subsequent transfer yields a cumulative pregnancy rate of 77%, a twin rate of less than 20%, and no triplet or higher-order pregnancies. CONCLUSION(S): The use of a cryopreservation program can help maximize pregnancy rates while minimizing multiple-pregnancy rates. Cryopreservation should be considered in all assisted reproductive technology cycles.