Background: Polycystic Ovarian Syndrome (PCOS) is a complex en- docrine disorder that affects women in their reproductive age. L-Carni- tine (LC) is a small water-soluble molecule that plays a basic role in the normal mitochondrial oxidation of fatty acids and generation of energy. Consequently LC is expected to play a positive role in enhancing ovari- an functions. This work was primarily designed to assess those positive effects of treatment with LC among adolescent PCOS patients. Objective: To assess the effect of treating adolescent PCOS patients with LC, in terms of improvement in menstrual irregularities, hormonal imbalance and body weight. Setting: Department of Obstetrics and Gynecology, Suez Canal Uni- versity Hospitals, Ismailia. Patients and Methods: This prospective randomized clinical trial in- cluded 25 adolescent PCOS patients with menstrual irregularity between the age of 14 and 19 years. They were given LC in a dose of 1 g daily for three months. Hormonal profile, menstrual pattern and body mass index (BMI) were assessed before and three months after treatment. Mainoutcomemeasures:Changes in menstrual cycle, hormonal profile and body weight. Results: The mean BMI decreased significantly after treatment from 29.34 ± 1.73 to 27.88 ± 1.45 (p value = 0.03). Prior to treatment, all the participants complained of menstrual irregularity, the most common form of menstrual irregularity was oligomenorrhea representing 56% (n=14) followed by irregular cycles (32% , n = 8 ) ,and finally secondary amen- orrhea (12% , n =3 ).After treatment with LC for 3 months 36% (n=9) of the study population regained regular cycles. Conclusion: Treatment of adolescent PCOS patient with LC help in re- gaining regular cycles and proved to be efficient in decreasing BMI and further large scale studies may be needed with larger sample sizes and more longer treatment period to elude all potential beneficial effects of LC in this age group.