Background: More than 1.5 million fractures occur due to osteoporosis each year. This study examines the annual health care utilization and associated expenditures of osteoporotic patients who sustain a new fragility fracture and of those without a new fracture. Methods and procedures: The study sample from commercial claims databases consisted of patients enrolled in US plans between January 1, 1997, and December 31, 2001. Patients with both an osteoporosis diagnosis and a related fracture were classified as osteoporosis with concurrent fracture; all other osteoporosis patients were classified as osteoporosis without concurrent fracture. Annual utilization and expenditures for the concurrent-fracture cohort were compared with those without concurrent fracture, as well as with a group of patients without osteoporosis (controls) that was matched to the concurrent-fracture cohort based on age, gender, US region, health plan type, and length of enrollment. Exponential conditional mean models were used to compute regression-adjusted total expenditures across the groups. The differences in adjusted expenditures were used to generate the economic burden-of-illness estimates. Results: Osteoporosis patients with concurrent fracture incurred more than twice the overall health care expenditures in the study period, compared with those without fracture (US 15,942 vs15,942 vs 6,476), and nearly three times those of the control group (US 15,942 vs15,942 vs 4,658). Approximately 25% of the overall health care expenditures (US 4,014 of4,014 of 15,942) for the concurrent-fracture group were osteoporosis-related expenditures, leading to the conclusion that comorbid conditions in osteoporosis patients with concurrent fracture contribute significantly to overall health care costs. Some of these comorbidity-related costs were likely due to pain-related disorders, which occurred significantly more frequently in the concurrent-fracture cohort than in the other groups. Conclusion: Osteoporosis-related expenditures, particularly those related to fracture, were substantial. However, non-osteoporosis-related expenditures to treat comorbid conditions constituted 75% of the overall health care costs in the year after an osteoporosis-related fracture, which warrants further investigation.