Background: Our objective was to evaluate the effect of ovarian endometrioma on ovarian stimulation outcomes in in vitro fertilization cycles (IVF). Materials and Methods: In this prospective cohort study, we followed 103 patients who underwent intra-cytoplasmic sperm injection (ICSI) procedures over a 24-months period. The study group consisted of 47 infertile women with either unilateral or bilateral ovarian endometrial cysts of less than 3 cm. The control group consisting of 57 patients with mild male factor infertility was candidate for ICSI treatment during the same time period as the study groups. Both groups were compared for number of oocytes retrieved, grades of oocytes, as well as embryo quantity and quality. Results: Our results showed similar follicle numbers, good embryo grades (A or B) and pregnancy rates in the compared groups. However, patients with endometrioma had higher gonadotropin consumption than the control group. The mean number of retrieved oocytes in patients with endometrioma was significantly lower than control group (6.6 ± 3.74 vs. 10.4 ± 5.25) (p<0.001). In addition, patients with endometrioma had significantly lower numbers of metaphase II (MII) oocytes (5 ± 3.21) than controls (8.2 ± 5.4) (p<0.001). In patients with unilateral endometrioma, there were no significant differences in main outcome measures between normal and involved ovaries in the patients with endometrioma. Conclusion: Patients with ovarian endometrioma had poor outcome. They showed poor ovarian response with lower total numbers of retrieved oocytes and lower MII oocytes during the stimulation phase; however, it does not affect the total number of embryos transferred per patient, quality of embryos, and pregnancy rate per patient
