Background: The study was performed to validate the threshold for anti-Müllerian hormone (AMH) that suggests the presence of polycystic ovaries in women with polycystic ovary syndrome (PCOS).Methods: This prospective observational study included 59 infertile women: (A) 22 PCOS with hyperandrogenism (HA) and oligo-anovulation, (B) 15 suspected PCOS with either HA or oligo-anovulation and (C) 22 asymptomatic control women. The diagnosis of PCOS was made according to the NIH classification.Results: For serum AMH and follicle number, respectively, the areas under the receiver operating characteristic curve (A versus C) were 0.97 and 0.93. The best compromise between specificity (95% and 91%) and sensitivity (95% and 82%) was obtained with threshold values of 33 pmol/l and 13 follicles, respectively. Using a serum AMH > 33 pmol/l as a surrogate for either HA or oligo-anovulation in group B would lead to the diagnosis of PCOS in seven (46.6%) patients from this group.Conclusions: Our data confirms that the AMH assay has a high diagnostic potential, providing that an appropriate threshold is used. AMH measurement may be included as an ultimate diagnostic criterion for the diagnosis of PCOS when either HA or anovulation is missing and/or when no reliable antral follicle count can be obtained.