The importance of serum estradiol changes associated with gonadotropin-releasing hormone antagonists is not clear. The purpose of the present study was to analyze the impact of estradiol changes after cetrorelix injection on the outcome of intracytoplasmic sperm injection (ICSI) cycles. This was a prospective observational study. One hundred and thirteen women with male-factor infertility who were undergoing first ICSI cycles were reviewed for this study. Excluding seven cycles with incomplete data, 106 cycles were included in the analysis. The women were stimulated with clomiphene citrate and human menopausal gonadotropin (hMG). Cetrorelix acetate (2.5 mg) was given when the leading follicles reached 14 mm. After cetrorelix administration, serum estradiol rose in 48 cycles (45.3%), plateaued in 26 cycles (24.5%) and dropped in 32 cycles (30.2%). Mean age and day-3 follicle-stimulating hormone, luteinizing hormone and estradiol levels were similar among the three groups. The mean ampoules of hMG used, estradiol levels on the day of human chorionic gonadotropin injection and the clinical outcomes, including numbers of oocytes retrieved and fertilization, implantation and pregnancy rates, were similar in all three groups regardless of the trend of estradiol. In conclusion, estradiol patterns after cetrorelix injection show no correlation with clinical outcome and ovarian reserve, and falling estradiol is not associated with adverse outcome.