Study ObjectiveTo evaluate the correlation between serum cystatin levels and clinical parameters in adolescents with polycystic ovary syndrome (PCOS). Design, Setting, Participants, Interventions, and Main Outcome MeasuresThis prospective case-control study included 89 adolescents with PCOS. Demographic characteristics and hormonal and biochemical parameters were compared between study (89 patients with PCOS) and control (84 subjects without PCOS) groups. Risk factors recorded were age, body mass index (BMI), waist to hip ratio (WHR), Ferriman–Gallwey score, triglyceride, total cholesterol, high-density lipoprotein, low-density lipoprotein (LDL), high-sensitivity C-reactive protein, cystatin C, follicle stimulating hormone, luteinizing hormone, estradiol, dehydroepiandrosterone sulfate, homeostatic model assessment insulin resistance index, free testosterone, and progesterone levels. ResultsBMI, WHR, Ferriman–Gallwey score, and triglyceride, LDL, total cholesterol, estradiol, dehydroepiandrosterone sulfate, free testosterone, luteinizing hormone, high-sensitivity C-reactive protein, and cystatin C levels, and homeostatic model assessment insulin resistance index scores were significantly higher, and high-density lipoprotein levels were lower in the PCOS patients compared with healthy subjects (P < .05). We also found positive correlations between the cystatin C levels and BMI, WHR, estradiol, high-sensitivity C-reactive protein, and LDL levels in the study group. ConclusionThe serum cystatin C level is a promising marker for diagnosing adolescent patients with PCOS and suggests an inflammatory etiology for these patients. Further studies with more participants should examine this potential association with inflammation.