In vitro, strontium ranelate increases collagen and noncollagen protein synthesis by mature osteoblast-enriched cells. Its effects on bone formation were confirmed as the drug enhanced preosteoblastic cell replication. In the isolated osteoclast, preincubation of bone slices with strontium ranelate-induced dose-dependent inhibition of the bone-resorbing activity of treated rat osteoclast. Strontium ranelate dose-dependently inhibited preosteoclast differentiation. Its effect in postmenopausal women with established osteoporosis was assessed during an international, prospective, double-blind, randomized, placebo-controlled phase 3 program comparing strontium ranelate 2 g daily with placebo. The 3-year analysis of the phase 3 study, Spinal Osteoporosis Therapeutic Intervention, evaluating the effect of strontium ranelate 2 g/day on vertebral fracture rates, revealed a significant 41% reduction in the relative risk of patients experiencing new vertebral fracture with strontium ranelate over 3 years. A second phase 3 study showed a significant reduction in the relative risk of experiencing a nonvertebral fracture in the group treated with strontium ranelate over 3 years. These results show that strontium ranelate is a new, effective, and safe treatment for vertebral and hip osteoporosis, with a unique mode of action, increasing bone formation and decreasing bone resorption leading to a rebalance of bone turnover in favor of bone formation.