Background: For women living with osteoporosis, high out-of-pocket (OOP) drug costs may prevent drug therapy initiation. We investigate the association between oral osteoporosis OOP medication costs and female Medicare beneficiaries' initiation of osteoporosis drug therapy. Methods: We used 2007 and 2008 administrative claims and enrollment data for a 5% random sample of Medicare beneficiaries. Our study sample included age-qualified, female beneficiaries who had no prior history of osteoporosis but were diagnosed with osteoporosis in 2007 or 2008. Additionally, we only included beneficiaries continuously enrolled in stand-alone prescription drug plans. We excluded beneficiaries who had a chronic condition that was contraindicated with osteoporosis drug utilization. Our final sample included 25,069 beneficiaries. Logistic regression analysis was used to examine the association between the OOP costs and initiation of oral osteoporosis drug therapy during the year of diagnosis. Findings: Twenty-six percent of female Medicare beneficiaries newly diagnosed with osteoporosis initiated oral osteoporosis drug therapy. Beneficiaries' OOP costs were not associated with the initiation of drug therapy for osteoporosis. However, there were significant racial disparities in beneficiaries' initiation of drug therapy. African Americans were 3 percentage points less likely to initiate drug therapy than Whites. In contrast, Asian/Pacific Islander and Hispanic beneficiaries were 8 and 18 percentage points, respectively, more likely to initiate drug therapy than Whites. Additionally, institutionalized beneficiaries were 11 percentage points less likely to initiate drug therapy than other beneficiaries. Conclusions: Access barriers for drug therapy initiation may be driven by factors other than patients' OOP costs. These results suggest that improved osteoporosis treatment requires a more comprehensive approach that goes beyond payment policies.