OBJECTIVE: To document the prevalence of polycystic ovary syndrome (PCOS) and its associated characteristics in a sample of urban Indigenous women. DESIGN: A cross-sectional survey of Indigenous women, including biochemical and anthropometric assessments. PCOS was assessed using the National Institutes of Health 1990 criteria. SETTING AND PARTICIPANTS: Indigenous women, aged 15-44 years, living in a defined area in and around Darwin, Northern Territory, Australia, September 2003-March 2005. MAIN OUTCOME MEASURES: Proportion of participants with PCOS overall and measures of obesity. RESULTS: Among 248 women eligible for assessment, the proportion who had PCOS was 15.3% (95% CI, 10.8%-19.8%). The proportion with PCOS was similar across age groups, but was significantly higher (P = 0.001) in women with a body mass index (BMI) of ≥ 30.0 kg/m(2) (30.5%) compared with women with a BMI of 25.0-29.9 kg/m(2) (8.2%) or a BMI of < 25.0 kg/m(2) (7.0%). CONCLUSIONS: A high proportion of these Indigenous women had PCOS. The significant relationship with obesity gives a strong rationale for screening for PCOS during routine care of Indigenous women who are obese and of reproductive age.