Polycystic ovary syndrome (PCOS) is a common endocrine metabolic disorder that is associated with high insulin resistance and obesity. However, ~70% of women with PCOS in Japan are non-obese. We retrospectively analyzed the cases of 163 Japanese women with PCOS who visited our Ob/Gyn department in 2006-2018 to determine which has a greater effect on insulin resistance: PCOS or obesity. We reviewed the women’s medical records and calculated their insulin resistance and insulin secretion.