Objective: To evaluate the rates of the CYP1A1 Ile/Val polymorphism in Turkish adolescent females. Methods: The CYP1A1 Ile/Val polymorphism was analyzed by collecting DNA samples from 44 adolescents with polycystic ovary syndrome (PCOS) according to the Rotterdam criteria and 120 healthy female controls aged 13-18 years in Ankara, Turkey. Results: There was a 2.5-fold increase in the frequency of the CYP1A1 Ile/Val genotype in adolescents with PCOS compared with the control group (odds ratio [OR] 2.54; 95% confidence interval [CI], 1.143-5.637; P<0.001), in addition to a 2.4-fold increase in the frequency of the Val allele (OR 2.43; 95% CI, 1.099-5.397; P<0.001). Conclusion: The data show an association between CYP1A and PCOS, indicating that variant alleles of the gene may affect the metabolic and transport pathway of estrogens, thus causing PCOS. (C) 2010 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved.