This study was performed to determine the significance of a baseline ovarian cyst on the response to controlled ovarian hyperstimulation and the outcome of IVF-ET. One hundred one patients who underwent IVF-ET were enrolled in this study. The outcome of 31 patients, who had an ovarian cyst of >10mm detected at ultrasound examination performed on day 3, was compared with that of 70 patients who underwent a similar protocol and did not have an ovarian cyst. E2 level on the day of hCG administration, the number of follicles, the number of oocytes retrieved, the number of embryo transferred and the pregnancy rate were evaulated. The E2 level on the day of hCG adminstration and the number of mature oocytes retrieved were lower in the group with a baseline cyst. The pregnancy rate also was significantly lower in the group with a cyst (21% versus 38%). Therefore a baseline ovarian cyst on cycle day 3 was associated with a poorer outcome after IVF-ET.