Objective: To investigate the predictive value of polycystic ovaries for endocrine signs of polycystic ovary syndrome (PCOS). Design: Controlled descriptive study. Setting: Academic tertiary care fertility clinic. Patient(s): Normogonadotropic (FSH levels between 1 and 10 mIU/mL, conversion factor to SI unit, 1.0) oligomenorrheic or amenorrheic women visiting our fertility clinic and a control group of regularly cycling, healthy, normal weight volunteers recruited by advertisement. Intervention(s): Single blood samples and transvaginal sonography were performed. Main Outcome Measure(s): Serum levels of FSH, LH, androstenedione (A), and T and ovarian volume, ovarian stroma density, and follicle number. Result(s): In control women, the 95th percentile was calculated for ovarian volume, follicle number, and stroma count as well as endocrine parameters. The use of these upper limits of normal in the study group resulted in 217 (66%) patients with polycystic ovaries on ultrasound (defined as increased mean ovarian volume and/or mean follicle number per ovary), whereas only 120 (36%) patients exhibited elevated serum androgens (increased A and/or T concentrations) and 155 (47%) showed elevated LH levels. Sensitivity and specificity of single or combined sonographic parameters for prediction of elevated serum LR or androgen concentrations were limited. Conclusion(s): In the study group of normogonadotropic oligomenorrhea or amenorrheic infertile women, we set strict cutoff levels for various criteria used in the literature for defining PCOS. Groups defined by sonographic or endocrine PCOS criteria did overlap, but sonographic parameters had limited predictive value for abnormal hormone serum levels.