Objective: Management of ovarian endometrioma before IVF treatment is still challenging. We aimed to assess the effect of the pre-cycle surgical removal of endometriomas on IVF outcomes in a large number of cycles in patients undergoing IVF/ICSI treatment. Besides this, we also proposed to compare the cycle outcomes within both normo and poor responder patients to evaluate the impact of endometrioma and its surgery. Study Design: A retrospective cohort study was conducted in a private IVF clinic between September 2014 and December 2018. A total of 2438 IVF/ICSI cycles of 1936 patients were reviewed. Patients who had previous endometrioma surgery (Group 1), patients with non-operated endometrioma (Group 2), and patients without endometriosis, including tubal factor infertility confirmed by laparoscopy and unexplained infertility without endometrioma (Group 3) were analyzed in this study. Results: Total dose of gonadotropins was significantly higher in group 1 than others (p < 0.05). However, antral follicle counts, estradiol levels on the day of hCG trigger, the number of retrieved and metaphase II oocytes were significantly lower in group 1 than in other groups (p < 0.05). Poor response to gonadotropins was more frequent in group 1 as compared to other groups (47.9%, 34.3%, 35.5%, respectively) (p < 0.05). Cycle cancellation rates were significantly higher in group 1 than in other groups (6.7%, 1.4%, and 2.8%, respectively) (p < 0.05). Clinical pregnancy (CPR) and live birth rates (LBR) per cycle and embryo transfer were not different among groups. However, CPR per cycle and embryo transfer were significantly higher in the operated endometrioma group within unexpected poor responders (p = 0.023, p = 0.010, respectively). CPR and LBR per cycle and per embryo transfer were similar within normoresponder patients. Multiple logistic regression analysis revealed that female age and poor response to gonadotropins were the significant variables in predicting live birth (OR: 0.946, CI: 0.926-0.966, p < 0.001 and OR: 3.294, CI: 2.336-4.645, p < 0.001, respectively). Conclusion: Pre-cyle removal of endometrioma may have an adverse impact on ovarian reserve, and pregnancy outcomes seem to be similar with or without surgery in patients undergoing IVF treatment. However, endometrioma surgery may be considered in the subsequent IVF cycles of patients with lower than expected ovarian response. (c) 2021 Elsevier B.V. All rights reserved.