Background: The mechanisms underlying the effect of estradiol (E2) on low-density lipoprotein cholesterol (LDL-C) levels are not completely understood, although a role for proprotein con-vertase subtilisin/kexin type 9 (PCSK9) has been proposed. We aimed to investigate the association between levels of E2, PCSK9 and lipid parameters in premenopausal women undergoing in vitro fertilization (IVF). Methods: Healthy women undergoing IVF in the Department of Obstetrics and Gynecology of the University General Hospital of Ioannina were recruited. Levels of E2, pro-protein convertase subtilisin/kexin type 9 (PCSK9), total cholesterol (TCHOL), high-density lip-oprotein cholesterol (HDL-C), LDL-C, and triglycerides (TGs) were measured 10 days after ovarian depression (E2min) and 7 days after ovarian stimulation (E2max). Results: A total of 34 consecutive healthy women aged 38 (26-46) years old who underwent a full IVF cycle were included. E2 levels increased by 329.6% from E2min to E2max (108 [47-346] to 464 [241-2471] pg/mL, p<0.05). At the same time, serum PCSK9 levels significantly decreased by 30.8% (245 ± 80 to 170 ± 64 ng/mL, p<0.05). No significant changes in TCHOL, LDL-C, TGs and HDL-C were found (-0.4%, -3.8%, -2.2%, and +5.3%, p >0.05). Conclusions: The increase in endogenous E2 production during an IVF cycle was associated with a significant decrease in serum PCSK9 levels during a 7-day period.