Purpose: To determine if important geographic differences exist in treatment rates for osteoporosis and whether this variation can be explained by regional variation in risk factors. Methods: The Global Longitudinal Study of Osteoporosis in Women is an observational study of women ≥ 55. years sampled from primary care practices in 10 countries. Self-administered questionnaires were used to collect data on patient characteristics, risk factors for fracture, previous fractures, anti-osteoporosis medication, and health status. Results: Among 58,009 women, current anti-osteoporosis medication use was lowest in Northern Europe (16%) and highest in USA and Australia (32%). Between 48% (USA, Southern Europe) and 68% (Northern Europe) of women aged ≥ 65. years with a history of spine or hip fracture since age 45 were untreated. Among women with osteoporosis, the percentage of treated cases was lowest in Europe (45-52% versus 62-65% elsewhere). Women with osteopenia and no other risk factors were treated with anti-osteoporosis medication most frequently in USA (31%) and Canada (31%), and least frequently in Southern Europe (12%), Northern Europe (13%), and Australia (16%). After adjusting for risk factors, US women were threefold as likely to be treated with anti-osteoporosis medication as Northern European women (odds ratio 2.8; 95% confidence interval 2.5-3.1) and 1.5 times as likely to be treated as Southern European women (1.5, 1.4-1.6). Up to half of women reporting previous hip or spine fracture did not receive treatment. Conclusions: The likelihood of being treated for osteoporosis differed between regions, and cannot be explained by variation in risk factors. Many women at risk of fracture do not receive prophylaxis. © 2011 Elsevier Inc.