Estimates of the prevalence of the polycystic ovary syndrome (PCOS) in the general population have ranged from 2-20%. The vast majority of these reports have studied White populations in Europe, used limited definitions of the disorder, and/or used bias populations, such as those seeking medical care. To estimate the prevalence of this disorder in the United States and address these limitations, we prospectively determined the prevalence of PCOS in a reproductive-aged population of 369 consecutive women (174 White and 195 Black; aged 18-45 yr), examined at the time of their preemployment physical. Body measures were obtained, and body hair was quantified by a modified Ferriman-Gallwey (F-G) method. All exams were initially performed by 2 trained nurses, and any subject with an F-G score above 3 was reexamined by a physician, the same for all patients. Of the 369 women, 277 (75.1%) also agreed to complete a questionnaire and have additional blood drawn. Subjects were studied regardless of current estrogen/progestin hormonal use (28.5%). PCOS was defined as 1) oligoovulation, 2) clinical hyperandrogenism (i.e. hirsutism) and/or hyperandrogenemia, and 3) exclusion of other related disorders, such as hyperprolactinemia, thyroid abnormalities, and nonclassic adrenal hyperplasia. Hirsutism was defined by a F-G score of 6 or more, and hyperandrogenemia was defined as a total or free testosterone, androstenedione, and/or dehydroepiandrosterone sulfate level above the 95th percentile of control values [i.e. all eumenorrheic women in the study, who had no hirsutism (F-G ≤5) or ache and were receiving no hormonal therapy; n = 98]. Considering all 369 women studied, White and Black women had similar mean ages (29.4 ± 7.1 and 31.1 ± 7.8 yr, respectively), although White women had a lesser body mass than Black women (24.9 ± 6.1 vs. 29.2 ± 8.1 kg/m2, respectively; P < 0.001). Of these 7.6%, 4.6%, and 1.9% demonstrated a F-G score of 6 or more, 8 or 10, respectively, and there was no significant racial difference, with hirsutism prevalences of 8.0%, 2.8%, and 1.6% in Whites, and 7.1%, 6.1%, and 2.1% in Blacks, respectively. Of the 277 women consenting to a history and hormonal evaluation, 4.0% had PCOS as defined, 4.7% (6 of 129) of Whites and 3.4% (5 of 148) of Blacks. In conclusion, in our consecutive population of unselected women the prevalence of hirsutism varied from 2-8% depending on the chosen cut-off F-G score, with no significant difference between White and Black women. Using an F-G score of 6 or more as indicative of hirsutism, 3.4% of Blacks and 4.7% of Whites had PCOS as defined. These data suggest that PCOS may be one of most common reproductive endocrinological disorders of women.