a b s t r a c t Objective: Patients with polycystic ovarian syndrome (PCOS) have a high prevalence of sleep disorders. Metformin is an antidiabetic drug that may have a role in treatment of the manifestations of PCOS. The aim of this study was to assess the presence of sleep disorders in adolescent girls with PCOS and to study the effects of using metformin on sleep disorders in these girls. Methods: This study was carried out on 90 adolescent girls aging from 12 to 18 years who were divided into 3 equal groups: control untreated group, untreated PCOS group, and PCOS þ metformin group. Body weight, height, body mass index, hirsutism score, fasting and postprandial blood glucose, fasting serum insulin, Homeostatic Model Assessment (HOMA) index, sleep disturbances scale, and Epworth sleepiness scale were measured. Results: Metformin administration resulted in significant decrease in the body weight, body mass index, hirsutism score, fasting and postprandial blood glucose, fasting serum insulin, HOMA index, sleep disturbances scale, and Epworth sleepiness scale compared to the untreated PCOS group. Conclusion: Metformin can reduce the incidence of sleep disorders and excessive daytime sleepiness in adolescent girls with PCOS. Key Words: Metformin, Sleep, Adolescent, PCOS