['To investigate the association of a common polymorphism of the interleukin-6 gene (IL6) promoter with the occurence and the clinical characteristics of polycystic ovary syndrome (PCOS).', 'Prospective, case-control study.', 'Academic research institution.', 'Sixty-two patients with PCOS and 94 healthy controls.', 'Peripheral venous puncture, ultrasonography, oral glucose tolerance test (OGTT), questionnaire.', 'Genotype analysis with respect to the common -174 G/C polymorphism of the IL6 gene promoter, analysis of testosterone (T), androstendione, and sex hormone binding globulin serum levels, and evaluation of the OGTT.', 'Allele frequencies among women with PCOS and controls were 62.9% and 64.4%, respectively, for the wild-type G allele, and 37.1% and 35.6%, respectively, for the mutant C allele. We ascertained a significant association between presence of at least one mutant C allele and the clinical characteristics of affected women: these women were more likely to present with a body mass index >27 kg/m(2), elevated total T serum levels, and a pathological OGTT result.'] Does a common interleukin-6 gene promoter polymorphism influence the clinical characteristics of women with polycystic ovary syndrome?