The objective of this study was to investigate the effect of luteinizing hormone levels on the day of human chorionic gonadotropin administration (late follicular phase) on ovarian response and pregnancy outcome in women receiving pituitary down-regulation with gonadotropin releasing hormone-agonist administration in a short protocol. Blood samples were collected from 74 women undergoing assisted reproduction and analyzed retrospectively. Based on luteinizing hormone levels on the day of human chorionic gonadotropin administration, patients were divided into two groups (＜5 and ≧5 IU/L). The number of follicles ≧15 mm in size and fertilized oocytes showed a highly significant correlation with luteinizing hormone concentration on the day of human chorionic gonadotropin administration. The levels of luteinizing hormone in the late follicular phase had a significant impact on the ovarian response and the quality of retrieved oocytes.