ABSTRACT Background: Polycystic ovary syndrome (PCOS) is considered the most frequent ovulatory disorder. PCOS often has a problem in (GnRH) release, with increase in the pituitary secretion of (LH) hormone and high LH/FSH ratio. Objective: The current study aimed at detecting the predictive level of LH/FSH ratio for the ovarian response, pregnancy and miscarriage rates in PCOS patients underwent mild ovarian stimulation. Patients and methods: A prospective cohort study was conducted in Gynaecology and Obstetrics Department, Zagazig University Hospitals. The study included PCOS women aged from 20 to 37 years, with at least 1 year of infertility, and normal semen analysis. The exclusion criteria were pelvic surgery and/or pathology. Cycle day 2-5 Serum LH and FSH were measured. Transvaginal ultrasound was done on cycle day 2-3 to prove quiescent ovaries, letrozole (2.5-5mg) was started from day 2-3 for successive 5 days with/without HMG (75-150IU/d) then follicular tracking was done till 1-3 follicles reached ≥18 mm upon which ovulation trigger was given. Results: A total 63 infertile women were included in the study. The mean age was 24.81 (SD 2.83) years, the mean BMI 30.65 (SD 6.58) Kg /m2. Basal FSH, LH level, and LH/FSH ratio ranged from 1.9-11.9 mIu/ml, 2.34-21 mIu/ml and 0.37- 4.63, respectively. ROC curve analysis showed LH/FSH ratio to be non-useful predictor of ovarian response, occurrence of pregnancy or miscarriage in PCOS patients underwent simple ovarian induction, AUC (0.51, 0.64 and 0.69 respectively). Conclusion: LH/FSH ratio seems to have no role in prediction of stimulated cycle outcome.