CONTEXT: The phenotype of women with polycystic ovary syndrome (PCOS) is variable, depending on the ethnic background. OBJECTIVE: The phenotypes of women with PCOS in Iceland and Boston were compared. DESIGN: The study was observational with a parallel design. SETTING: Subjects were studied in an outpatient setting. PATIENTS: Women, aged 18-45 yr, with PCOS defined by hyperandrogenism and fewer than nine menses per year, were examined in Iceland (n = 105) and Boston (n = 262). INTERVENTION: PCOS subjects underwent a physical exam, fasting blood samples for androgens, gonadotropins, metabolic parameters, and a transvaginal ultrasound. MAIN OUTCOME MEASURES: The phenotype of women with PCOS was compared between Caucasian women in Iceland and Boston and among Caucasian, African-American, Hispanic, and Asian women in Boston. RESULTS: Androstenedione (4.0 +/- 1.3 vs. 3.5 +/- 1.2 ng/ml; P