OBJECTIVES: To determine the number of women in France at least 50 years of age with risk factors for osteoporosis likely to lead to bone mineral density measurement, an investigation reimbursed by the French national health insurance system in patients at risk for osteoporosis. The study was commissioned by the French health authorities. MATERIALS AND METHODS: Risk factors for osteoporosis were defined as recommended by the French Agency for Accreditation and Evaluation in Health (ANAES) in 2001. The study data were from nine cohort studies done in France and from the National Health Insurance Agency for the Rhone-Alpes region of France. Risk factor prevalences in France were standardized by extrapolation according to the age distribution in France. RESULTS: Overall, data were collected in 123,986 women aged 50 years or older. From these data, risk factor estimates were as follows: menopause before 40 years of age, 1.5 million women; body mass index (BMI) lower than 19 kg/m(2), nearly 700,000; history of fracture, more than 2 million; history of femoral neck fracture in the mother, more than 1 million; history of health problems potentially responsible for osteoporosis, 400,000; and history of long-term glucocorticoid therapy, 612,000. In all, 3,186,318 (30%) women were estimated to have at least one risk factor and 785,512 (7.5%) at least two risk factors. CONCLUSIONS: Although our study sample was not representative of the population residing in France, the large sample size and diversity of data sources support the validity of our estimate of the prevalence of risk factors for osteoporosis in postmenopausal women living in France.