Background: PCOS is a common endocrine disorder of reproductive age with high morbidity that its prevalence ranging from 5.6% to 26%. The aim of this study was to evaluate the prevalence of PCOS in Iranian adolescent girls aged 14-19 years based on adults and adolescents’ criteria. Methods: This cross-sectional study was carried out with 650 high school adolescent girls in Mashhad city, north-east of Iran. PCOS was defined as the presence of three or two of the three features including oligo/amenorrhea, clinical or biochemical hyperandrogenism, and polycystic ovaries. Descriptive statistics, chi-square, and t-test were used to analyze the data through SPSS vs 22 (SPSS Inc., USA) and the significance level was set at p≤0.05. Results: The mean age of adolescent girls was 16.73±3.4 years. The prevalence of PCOS using Rotterdam, National Institutes of Health (NIH), Androgen Excess– PCOS Society (AES), European Society of Human Reproduction and Embryology (ESHRE)/American Society for Reproductive Medicine (ASRM) (2012), and Endocrine Society Clinical Practice (2013) criteria was 4.2%, 3.6%, 3.6%, 0.7%, and 3.6%, respectively. Conclusion: The rate for prevalence of PCOS calculated based on Rotterdam, NIH, AES, and Endocrine Society (2013) criteria was higher in comparison to ESHRE/ ASRM (2012) criteria. According to the results of our study, in order to prevent overestimation of this syndrome’s prevalence in the adolescents due to its overlap with signs of pubertal development, all above-mentioned three criteria should be considered together, which is in line with the recommendations proposed by Carmina et al. and ESHRE/ASRM working group.