Objective: To test the hypothesis that the polycystic ovary syndrome (PCOS) phenotype, or its component features, is less severe in adolescents than in young adult patients, in a referred (clinical) population. Design: Cross-sectional study. Setting: Tertiary-care academic medical center. Patient(s): Two hundred seventy-four adolescents and young adults aged 13.0–24.9 years with PCOS according to the National Institute of Health 1990 criteria. Patients were categorized as adolescents (AD: 13.0–18.9 years; n = 91) and young adults (YA: 19.0–24.9 years; n = 183). Adolescents were further categorized as early adolescents (Early-AD: 13.0–15.9 years; n = 31) and late adolescents (Late-AD: 16.0–18.9 years; n = 60). Intervention(s): History, physical examination, hormonal assays with the use of standardized protocols. Main Outcome Measure(s): Unadjusted and adjusted odds ratios (ORs; adjusted for body mass index [BMI] when applicable) were calculated for biochemical hyperandrogenism (HA), hirsutism (HIR), acne, and degree of oligo/amenorrhea (OA). PCOS phenotypes were classified as HIR+HA+OA, HA+OA, and HIR+OA. Result(s): Our analysis demonstrated minimal significant difference in the prevalence of the three PCOS phenotypes, or component features, between AD and YA patients. The risks for obesity were higher for YA versus AD, and the risk of acne was lower for YA versus AD. There was no significant difference between Early-AD and Late-AD. BMI-adjusted models did not significantly modify the main findings. Conclusion(s): The present study suggests that the PCOS phenotype is established in early adolescence, remains constant into adulthood, and is not related to BMI.