OBJECTIVE: To evaluate LH levels in women with the classic (1990 criteria) and the newer (2003 criteria) PCOS phenotypes, and to examine the impact of BMI and insulin resistance indices on hormone levels.STUDY DESIGN: In this controlled clinical study 936 women with PCOS, classified as classic (n=729) and newer (n=207), and 204 controls were included. All women were divided into normal-weight (BMI<25 kg/m(2)) and overweight plus obese (BMI≥25 kg/m(2)). Serum LH, FSH, anthropometrics, androgens, fasting insulin and glucose, HoMA-IR, number of follicles, and ovarian volume were assessed.RESULTS: Women with classic PCOS presented significantly higher LH and LH/FSH ratios, and lower glucose/insulin levels than those with the newer phenotype and controls. Overweight plus obese women of all groups had lower LH levels than normal-weight women. Independent positive correlations between LH and androgens and negative correlation between LH and BMI were found.CONCLUSIONS: The higher LH concentrations of the classic phenotypes of PCOS could be attributed to the higher androgen levels, which desensitize the hypothalamus to the negative feedback regulation by progesterone. Moreover, the lower LH levels of overweight plus obese women of all groups could be attributed to the increased peripheral aromatization of androgens to estrogens in adipose tissue leading to suppression of LH secretion.CONDENSATION: Both normal-weight and overweight women with classic PCOS phenotypes present higher LH levels and LH-to-FSH ratios than women with similar BMI but the newer phenotypes.