OBJECTIVE: To determine whether endometrial echogenicity, assessed objectively by a computer-assisted system on the day of hCG administration, predicts endometrial receptivity in controlled ovarian hyperstimulation (COH) cycles for IVF-ET. DESIGN: Prospective analysis. SETTING: Assisted reproduction unit, Clamart, France. PATIENT(S): Two hundred twenty-one women (aged <38 years with a normal uterus and >/=2 grade A or B embryos transferred) undergoing 228 GnRH agonist and FSH/hCG cycles for IVF-ET. INTERVENTION(S): On the day of hCG administration, uterine ultrasound scans were digitized with an image analysis system. Endometrial echogenicity was assessed as the ratio of the extent of the hyperechogenic transformation over the whole endometrial thickness. According to this, cycles were sorted arbitrarily into six groups: <30% (n = 34), 31%-40% (n = 37), 41%-50% (n = 37), 51%-60% (n = 55), 61%-70% (n = 37), and >70% (n = 28). MAIN OUTCOME MEASURE(S): Pregnancy and implantation rates. RESULT(S): The groups were similar in regard to population characteristics, ovarian response to COH, and embryology data. Pregnancy rates (59%, 57%, 35%, 20%, 16%, and 11%, respectively) and implantation rates (35%, 23%, 17%, 6%, 7%, and 3%, respectively) fell progressively and significantly from the low-echogenicity group to the high-echogenicity group. CONCLUSION(S): The present results confirm and extend previous observations that advanced hyperechogenic transformation of the endometrium is associated with poor IVF-ET outcome.