Context: Nowadays, the main cause of infertility is ovulatory. Its treatment requires ovulation induction either in order to obtain monoovulation or controlled ovarian hyperstimulation within the assisted human reproduction protocols. Aromatase inhibitors are successfully used for monoovulation induction. Objective: The aim of the study is to assess the effectiveness of Letrozole in inducing monoovulation in women with ovarian dysfunction. Methods: We conducted a retrospective clinical study in patients with infertility who received Letrozole for monoovulation induction. Patients: Patients were divided into two groups according to the cause of ovarian dysfunction, hormonal profile, antral follicle count and medical history. We didn’t include in the study patients who associated tubal dysfunction or male causes of infertility. Intervention: 2.5mg or 5mg per day of Letrozole was administered for five days in early follicular phase and we monitored the follicular growth as well as endometrial thickness and quality. This therapy was followed by ovulation triggering for directed sexual intercourse or artificial insemination with freshly prepared sperm. Results: Following ovarian stimulation with aromatase inhibitors, ovulation was achieved in all patients, and more than half of them achieved a pregnancy. Most of the pregnancies had a normal evolution until birth and the newborns were healthy. A particularity of the patients in the study was an average of 4-year infertility duration with many previous ovarian stimulation treatments. Conclusions: Aromatase inhibitors are a valid option for the treatment of infertility, especially in patients with relatively low ovarian reserve. The advantages of this therapy compared to ovarian stimulation protocols with clomiphene citrate or gonadotropins are: obtaining monoovulation, good quality endometrium and low risk of ovarian hyperstimulation syndrome.