BACKGROUND: Relatively few patients have dual-energy x-ray absorptiometry to quantify the magnitude of bone loss as they age. Recent work correlates mean computed tomography (CT) attenuation in the level I (L1) vertebra with bone mineral density (BMD), making it possible to objectively evaluate the magnitude of bone loss in osteoporosis by this method. The aims of this study were to evaluate the utility of using CT scans in patients with acute thoracic and lumbar spine fractures to diagnose osteoporosis and using CT attenuation to evaluate the association between age and BMD. METHODS: We performed a retrospective study of patients with acute fractures of the thoracic or lumbar spine who had also undergone an abdominal (or L1) CT scan and compared mean CT attenuation in L1 against threshold values. We also compared differences in CT attenuation between younger (<65 years) and older (>/=65 years) and older patients. RESULTS: A total of 124 patients were evaluated (74 thoracic and 50 lumbar fractures). Overall, there was a strong correlation between age and bone density as measured by CT attenuation (r = -.76). Among those with thoracic fractures (<65 years), mean CT attenuation was 196.51 HU. Forty-one patients were >/=65 years and had mean CT attenuation of 105.90 HU (P < .001). In patients with lumbar fractures, 27 patients were <65 years and had a mean CT attenuation of 192.26 HU and 23 patients were >/=65 years and had mean CT attenuation of 114.31 HU (P < .001). At the threshold of 110 HU, set for specificity, the magnitude of difference between the age-stratified cohorts was greater in the thoracic spine (P < .0001 vs P = .003). DISCUSSION: Using opportunistic CT, we demonstrate the relative frequency of osteoporosis in patients with acute fractures of the thoracic and lumbar spine and confirm that the association increases with age. The CT attenuation may provide a cheap and convenient method to help confirm a clinical diagnosis of osteoporosis in patients with fractures.