Empty follicle syndrome (EFS) has been defined as a condition where no oocytes can be retrieved for in vitro fertilization (IVF) even though ultrasound findings and estradiol (E) levels suggest the presence of potential follicles. The EFS is a rare condition with an incidence of 0.5-7 % of women undergoing IVF treatments. Although there are many hypotheses as to the cause of EFS, including advanced ovarian age, drug-related problems, and dysfunctional folliculogenesis, its cause remains unknown. A 37-year-old woman with endometriosis and a 5-year history of primary infertility underwent IVF treatment for 4 cycles. No oocytes were retrieved in 2 cycles and no fertilized eggs were obtained in the other 2 cycles. We assumed that endometriosis adversely affected folliculogenesis and fertilization. Aspiration of an endometrial cyst in the right ovary and subsequent administration of oral contraceptives resulted in successful folliculogenesis and fertilization. Thereafter, she conceived and delivered a 2,662 g female infant at 38 weeks of gestation. Here, we report a case of EFS who conceived in the 5th IVF cycle after aspiration of an endometrial cyst. We assumed that endometriosis might have been involved in the dysfunction of folliculogenesis and EFS.

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