Objective: This study aimed to evaluate the efficacy of short and extended long course of letrozole therapy for ovulation induction in clomiphene resistant women with polycystic ovary syndrome. Patients:  One hundred infertile women were selected from the patients attending the outpatient clinic of Manshiet El-Bakry general hospital. All patients were diagnosed as having anovulation due to polycystic ovary syndrome (PCOS). Interventions: Patients were randomly allocated to treatment with either long letrozole  group took 2.5 mg of letrozole daily starting day 1 of spontaneous or progesterone inducing menstrual bleeding for 10 days (50 patients, up to 3 cycles) or short letrozole group  took 5 mg of letrozole daily starting day 1 of spontaneous or progesterone inducing menstrual bleeding for 5 days (50 patients, up to 3 cycles). Results:The number of ovulating patients was greater in the long letrozole group (74% vs. 56%), but without statistical differences. The total number of follicles during stimulation was insignificantly greater in the long letrozole group (8.2 vs. 8.17). The numbers of follicles ≥18 mm were significantly greater in the long letrozole group.  Pregnancy occurred in 7 in the short group (14%) and 12 of (24%) in the long letrozole group, and the difference was statistically insignificant. Conclusion:  The long letrozole protocol (10 days) can produce more mature follicles and subsequently more pregnancies than the short letrozole therapy (5 days).