 This prospective randomized trial included 136 anovulatory women with CC-resistant PCOS among those attending the Gynecology Outpatient Clinics of, Benha University Hospital, and private practice settings, Alkalubia, Egypt from August 2012 to August 2014. The study protocol was approved by the Local Ethics Committee and written informed consents were obtained before the study commenced. Diagnosis of PCOS was based on the Rotterdam criteria 18, whereby diagnosis of PCOS require the presence of two of three criteria after the exclusion of other etiologies, i.e., oligomenorrhea andor anovulation, clinical andor biochemical signs of hyperandrogenism, andor polycystic ovaries on ultrasound. Inclusion criteria: 1- Age: between 18-35 years. 2- Period of infertility 2 years. 3- Serum level of FSH 10 UL in the early follicular phase. 4- All women were CC-resistant PCOS, as they failed to ovulate with a dose of CC of 150 mgday for 5 days per cycle for at least three consecutive cycles. 5- All women had patent Fallopian tubes proved by hysterosalpingography or laparoscopy and their partners satisfied the normal parameters of semen analysis according to the modified WHO criteria 19. Exclusion criteria: 1- Infertility due to causes other than CC- resistant PCOS or due to combined factors. 2- Body mass index BMI 35 Kgm2. 3- The use of metformin, gonadotropins, hormonal contraception or diet regimen within the last 6 months. 4- Women with congenital adrenal hyperplasia, hyperprolactinaemia or abnormal thyroid function. 5- Hypersensitivity or contraindications to Letrozole or clomiphene treatment. 6- Previous LOD. The study was started two months after last CC treatment cycle to eliminate any post-treatment effect of CC. 