<p>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&rsquo; criteria.<br /> 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 <em>vs </em>22 (SPSS Inc., USA) and the significance level was set at p&le;0.05.<br /> Results: The mean age of adolescent girls was 16.73&plusmn;3.4 years. The prevalence of PCOS using Rotterdam, National Institutes of Health (NIH), Androgen Excess&ndash; 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.<br /> 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&rsquo;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.</p>