Teriparatide is the first bone-building drug available for the treatment of osteoporosis. We investigated the efficacy of this compound as assessed by spinal deformity index (SDI) using data from the Fracture Prevention Trial (FPT). The FPT was a randomized, double blind trial of placebo versus teriparatide 20 microg (TPTD20) versus teriparatide 40 microg (TPTD40) administered by daily self-injection. Patients included in the current analyses were those patients from the placebo (n = 398) and TPTD20 (the approved dose, n = 403) groups with baseline and follow-up radiographs and at least one vertebral fracture at baseline. For each vertebra, a visual semiquantitative grade of 0, 1, 2, or 3 was assigned for no fracture or mild, moderate, or severe fracture, respectively; the SDI was calculated by summing the fracture grades of all T4 to L4 vertebrae. The mean SDI increased in the placebo and TPTD20 groups by 0.485 and 0.134, respectively (P < 0.001). The proportions of patients with SDI increases >1, >2, and >3 were reduced by 85%, 80%, and 80%, respectively. In the placebo group, increasing baseline SDI was correlated with the mean increase in SDI during the trial (r = 0.080, P = 0.01), consistent with the progressive natural history of osteoporosis. However, in the TPTD20 group, increasing baseline SDI was not correlated with the mean increase in SDI during the trial (P = 0.297) indicating that teriparatide mitigated or eliminated the increased risk associated with increasing fracture burden. Increases in SDI during the trial were associated with increasing proportions of patients with new or worsening back pain and greater mean height loss (P < 0.0001), demonstrating an association with important clinical consequences. The results indicate that teriparatide greatly reduced the increase in fracture burden in the FPT and mitigated or eliminated the risk for future fractures imparted by increasing baseline fracture burden.