OBJECTIVE: The objective was to compare the efficacy of bisphosphonates regarding the prevention of vertebral fractures in postmenopausal women with osteoporosis. METHODS: Seven randomized placebo controlled trials investigating the effects of zoledronic acid (one study), alendronate (three studies), ibandronate (one study), and risedronate (two studies) in terms of fractures with a follow-up of 3 years were identified with a systematic literature search. The endpoint of interest was vertebral fractures. Results of all trials were analyzed simultaneously with a Bayesian mixed treatment comparison (MTC). With MTC the relative treatment effect of one intervention to another can be obtained in the absence of head-to-head evidence. MTC can be considered a valid method when included studies are comparable regarding effect modifying baseline patient and study characteristics. RESULTS: There is a 98% probability that zoledronic acid shows the greatest reduction in vertebral fractures of all four bisphophonates compared. Zoledronic acid showed an OR of 0.28 (95% Credible Interval 0.22; 0.35) relative to placebo, an OR of 0.57 (0.36; 0.92) relative to ibandronate, an OR of 0.54 (0.39; 0.75) relative to alendronate, and an OR of 0.49 (0.34; 0.69) relative to risedronate. Alendronate, ibandronate, and risedronate showed comparable vertebral fracture reductions. Indirect comparisons using a conservative random effects model supported these findings. CONCLUSION: An indirect comparison of findings from placebo controlled randomized studies indicates that zoledronic acid provides a greater vertebral fracture risk reduction in postmenopausal women with osteoporosis than ibandronate, alendronate, or risedronate.