Objective: To determine the prevalence of clinical polycystic ovary syndrome (PCOS) in 14- to 18-year-old high school girls in Isfahan, Iran. Methods: In this cross-sectional study, 1,000 high school girls (14–18 years old) were selected by multi-stage random sampling from different high schools in Isfahan. Following physical examination, a single physician recorded the presence of hirsutism, severe acne, androgenic alopecia, menstrual dysfunction and obesity using a validated questionnaire. Clinical PCOS was diagnosed if menstrual dysfunction and clinical hyperandrogenism were detected. Results: Clinical PCOS was present in 30 (3%), hirsutism in 60 (6%), menstrual dysfunction in 74 (7.4%) and severe acne in 47 (4.7%) of the population studied. Conclusion: The prevalence of clinical PCOS in our study population was similar to those of other studies; however, the prevalence could have been higher with hormonal assessment.