Assisted reproductive technology procedures infrequently cause pelvic abscesses, but the risk is higher in patients with endometriosis. If antibiotic treatment of a pelvic abscess is unsuccessful, surgery is required-even during pregnancy. We report two patients with endometriosis who suffered from pelvic abscesses formed after egg collection and embryo transfer. Patient 1 underwent laparoscopic resection of the left adnexa and right ovarian cystectomy after diagnosis of the implantation failure. Surgical findings showed severe adhesions in the pelvis due to endometriosis. Patient 2 underwent open drainage surgery at 11 weeks of pregnancy due to pan-peritonitis caused by a pelvic abscess. The patient delivered at 36 weeks of gestation. We conclude that egg collection and embryo transfer in patients with endometriosis confers a high risk for pelvic infection. An accurate diagnosis and appropriate treatment, including surgery, are mandatory in case of severe pelvic abscesses during pregnancy to save both mother and fetus.