The aim of this study was to examine the effects of risedronate (5 mg/daily) in patients identified solely on the basis of a prior fragility fracture, without BMD as an inclusion criterion. A total of 1,802 patients were examined from the VERT-NA and VERT-MN clinical trials. Lateral radiographs (T4 to L4) were obtained at baseline and annually; incident fractures were evaluated using quantitative and semiquantitative methods at the central facility. BMD was measured at the lumbar spine and femoral neck by dual-energy X-ray absorptiometry. Secondary analyses evaluated vertebral fracture efficacy in patient subgroups categorized according to the presence of risk factors for osteoporosis at baseline (age, femoral neck BMD, lumbar spine BMD, more severe BMD, height, weight, body mass index, prevalent nonvertebral fracture status, smoking, and bone turnover marker levels). Over 3 years, risedronate reduced the risk of new vertebral fractures by 44% (95% CI, 28% to 56%) compared with placebo. In patients subgrouped according to the presence or absence of putative risk factors, the efficacy of risedronate was comparable across all groups (all treatment-by-non BMD subgroup interactions p > or =0.210). Adjustment for age, baseline BMD, and prevalent vertebral fractures on fracture risk gave results similar to the unadjusted analysis. In patients taking placebo, the incidence of new vertebral fracture was higher in several of the high-risk categories (elderly, T-score < or = -2.5 SD). In conclusion, the findings of this study suggest that risedronate is effective in patients identified solely on the basis of a prior fragility fracture and that the efficacy of risedronate in the reduction of vertebral fractures is largely independent of the presence of clinical risk factors for osteoporotic fracture.