Background: Infertility is defined as failure to achieve pregnancy within 12 months of unprotected intercourse or therapeutic donar insemination in women younger than 35 years or within 6 months in women older than 35 years. In WHO classification of anovulation, Group 2 i.e. Hypothalamic-pituitary dysfunction is most common which is characterized by irregular or anovulatory menses, normal FSH, estrogen, and prolactin. Letrozole , is third generation, potent , reversible non steroidal aromatase inhibitor plays a pivotal role in the treatment of anovulatory infertility. Due to negative feedback FSH and LH level increases which leads to recruitment and growth of antral follicles. The short term regimn letrozole approach ovulation with minimal risk of adverse effect on endometrium thereby preserving endometrial receptivity and optimising condition for embryo implantation. use of extended regimn letrozole lies its ability to maintain low estrogen levels and sustain the inhibitory effect on aromatase enzyme activity throughout the follicular phase ,thereby promoting follicular growth and enhancing the likelihood of achieving a mature dominant follicle. Objective: A Comparative Study of the efficacy of fertility outcome by short term letrozole versus extended letrozole regime in infertile patients with anovulatory cycles. Method: This is a prospective comparative study comprising of 80 women with anovulatory cycles attending the gynaecology OPD in Department of Obstetrics and Gynaecology, of F.H.M.C. Etmadpur ,Agra from the period Jan 2023 to Dec 23. After full filling the inclusion criteria total number of participants divided in two group each having 40 participants. Group A – Extended protocol 2.5mg/day X 10days (D1-D10 of menses),.Group – Short protocol 5mg/day X 5days (D2-D7 of menses). Patients were followed from day 11 of the menses for follicular monitoring via USG till dominant follicle become 18 mm in size and a trigger of hcg 5000IU given i/m and rupture of follicle is monitored. Patient is followed after 14 days of trigger with UPT report. Outcome was measured in term of viable pregnancy. Result: Thisstudy suggest that extended letozole therapy shows more no of growing follicles, more ovulation rate ,more no of pregnancy but data is not statistically significant. Conclusion: It was accepted that by extending the letrozole therapy in midfollicular phase would maintain the FSH window prolonged allowing multifolliculardevelopement. this extended protocol appears to be more effective than the conventional short protocol with more no of matured follicles and more clinical pregnancy rate