Background: Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women and cause of infertility due to lack of ovulation. The symptoms of PCOS are observed during puberty and it is assumed that the weight gain during this period to be associated with this syndrome.Objective: To determine the prevalence of phenotypes of polycystic ovary syndrome in adolescents in Shiraz.Methods: This was a cross-sectional study in which 3190 female adolescents aged between 14 to 18 years, randomly selected from high schools in Shiraz, were studied. Diagnosis of PCOS was achieved through taking history and examination based on presence of oligomenorrhea (six times menstrual cycles or less in one year), clinical signs of hyperandrogenism including hirsutism (Ferriman-Gallway scores of 6 or more), severe acne, male pattern hair loss, and ultrasonography. The hormone dehydroepiandrostandion sulfate levels were measured for all subjects. Data were analyzed using the chi square test and Fisher's t exact-test.Findings: The prevalence of PCOS phenotypes were as follows: clinical hyperandrogenism and oligomenorrhea 19.9% (29 cases), clinical hyperandrogenism and polycystic ovary 30.8% (45 cases), oligomenorrhea and polycystic ovary 29.5% (43 cases), and clinical hyperandrogenism with oligomenorrhea and polycystic ovary 14.5% (21 cases). The frequency of highest levels of dehydroepiandrostandion sulfate was observed in patients with oligomenorrhea and hyperandrogenism.Conclusion: The risks of sex hormones turmoil, psychological effects of skin symptoms (acne and hirsutism), and numerous side-effects of this syndrome make it necessary to perform an early investigation in target population.