Objective: To evaluate serum anti-Mullerian hormone (AMH) levels in adolescent and young adult (AYA) Turkish patients with Polycystic ovary syndrome (PCOS), and to determine whether it had a diagnostic value. Materials and Methods: A total of 90 AYA patients were recruited for this study. The study group consisted of 43 patients diagnosed as having PCOS, and the control group comprised 47 age-matched patients. The diagnosis of PCOS was made in accordance with the recent Amsterdam European Society of Human Reproduction and Embryology/American Society for Reproductive Medicine PCOS consensus workshop group’s proposal that all three of the Rotterdam criteria for diagnosing PCOS in adolescents be present. In all patients, serum AMH levels were measured using enzyme-linked immunosorbent assay. Receiver operator characteristics (ROC) curve analysis was performed to reveal diagnostic potential of AMH. Results: Serum AMH levels were higher in the PCOS group compared with controls, but the difference was not statistically significant (10.1±6.9 ng/mL vs. 9.4±5.5 ng/mL, p=0.198). There was a significant age-related decrease in AMH levels in both the study and control groups (r=-0.331, p=0.001). There was also a significant inverse correlation between serum AMH and follicle-stimulating hormone levels in all patients (r=-0.227, p=0.031). ROC analyses demonstrated that the area under the curve indicative of AMH value for discriminating PCOS was 0.579 with a 95% confidence interval of 0.453-0.705 (p=0.198). The cut-off value according to the highest Youden index was calculated to be 14.0 ng/mL with a sensitivity of 48.8% and specificity of 77.1%. Conclusion: Serum AMH levels are slightly higher in AYA patients with PCOS than in controls. However, AMH is not a good marker for the diagnosis of PCOS in AYA patients.