This study was designed to compare the effectiveness of clomiphene, tamoxifen and letrozole in ovulation induction outcome: number of mature follicles, endometrial thickness, pregnancy rate, multiple pregnancy rate, live birth and miscarriage in isolated non PCOS unovulatory patient. In this prospective randomized clinical trial, 150 infertile women who had isolated nonPCOS unovulation, were randomized to 3 groups. Group A received clomiphene, 50 mg up to 150mg for 5-7days. Group B received tamoxifen 10 mg up to 30mg for 5-7 days and Group C received letrozole 2.5 mg up to 7.5mg for 5-7 days. The drugs have been increased in dose and duration to achieve mature follicle. If the patients were not responding to treatment with maximum dose for 7 days or failed to concept after six months, treatment was discontinued. Main outcome measures were number of follicles ≥18 mm, endometrial thickness and ovulation rate and secondary outcome measures clinical pregnancy rates, spontaneous abortions rates, multiple pregnancies, and ovarian hyperstimulation syndrome (OHSS).