The use of historical controls may be a viable alternative for comparing antifracture efficacy in osteoporosis fracture endpoint trials that do not have a placebo control group. The risedronate 2 consecutive days a month (2CDM) study showed that risedronate 75mg on 2 consecutive days had similar increases in bone mineral density compared with risedronate 5mg/d. To assess the antifracture efficacy of this regimen, data collected in the 2CDM study were analyzed using historical control data matched for key clinical characteristics from 2 placebo-controlled trials. Fracture rates in historical groups were compared with those of the 2CDM study treatment groups. At 12mo, vertebral fractures occurred in 5.1% and 1.0% of the placebo and 5-mg risedronate historical patients, respectively. In the risedronate 5mg/d and 75mg 2CDM groups, fracture incidence was 1.5% and 1.1%, respectively. Based on comparisons with the historical control group, risedronate 75mg 2CDM appears as effective as the 5-mg/d dose in reducing the risk of new vertebral fractures in the first year of treatment. The use of appropriate historical control data may provide an alternative design to assess fracture effects in osteoporosis trials for which simultaneous placebo-controlled data are unavailable.