PURPOSE: The reduction of the number of embryos transferred while maintaining a satisfactory rate of pregnancy (PR) with in vitro fertilization calls for a refined technique of embryonic selection. This prospective study investigates the significance of early embryonic compaction at day 3 as a marker of the chances of implantation. METHODS: We examined 317 transfers and their outcome involving 509 embryos including 91 compacted embryos. RESULTS: Early compaction seems linked with the ovarian response to stimulation and embryonic quality. The PR is significantly increased when the embryonic cohort contains at least one compacted embryo (44% versus 29.5%, p = 0.01), and when at least one compacted embryo is transferred (44% versus 31%, p < 0.05). The analysis of our single embryo transfers shows that the implantation rates are significantly better for compacted embryos (50% versus 30%, p < 0.05) (OR 2.98; CI 1.02-5.28). CONCLUSION: Thus, early compaction, sometimes observed at day 3, may serve as a useful additional criterion for selecting the embryos transferred.