Objective: To examine sperm DNA fragmentation in semen used for assisted reproduction procedures to establish this factor's prognostic role in fertilization rate, embryo development, pregnancy rate, and outcome. Design: Prospective study. Setting: Department of Medicine and Biology of Reproduction of the Edouard Herriot Hospital in Lyon, France. Patient(s): 322 couples, divided into 88 cycles of in vitro fertilization (IVF) or 234 cycles of intracytoplasmic sperm injection (ICSI). Intervention(s): Sperm DNA fragmentation was detected in sperm obtained 2 to 5 months before the ART procedure. Main Outcome Measure(s): Sperm DNA fragmentation was measured with the terminal deoxynucleotidyl transferase-mediated digoxigenin-dUTP nick-end labeling (TUNEL) technique. Result(s): There was a negative statistical correlation between the rate of fragmentation and the semen characteristics. A statistically significant negative relationship was found for sperm DNA fragmentation and fertilization when ICSI and IVF were compared. With ICSI, a statistically significant negative relationship was found between fertilization rate and percentage of sperm DNA fragmentation (DNA fragmentation index, or DFI). The risk of nontransfer due to blocked embryo development increased when the DFI exceeded 15% (18.2% for ICSI vs 4.2% for IVF) with an odds ratio of 5.05. The miscarriage risk increased four fold when the DFI exceeded 15% (37.5% for ICSI vs 8.8% for IVF). Conclusion(s): Sperm DNA fragmentation measured 2 to 5 months before the assisted reproduction procedure was a prognostic indicator of the fertilization, pregnancy, and miscarriage rates and the pregnancy outcome.