1404 patients with bone metastases from breast cancer were randomized to receive treatment with either oral ibandronic acid or intravenous zoledronic acid. The frequency and timing of skeletal-related events (SREs) was the primary non-inferiority endpoint. After 96 weeks of treatment, 50 mg of oral ibandronic acid given daily was inferior to 4 mg of intravenous zoledronic acid given every 4 weeks in preventing SREs. Although ibandronic acid was associated with fewer renal toxic effects than zoledronic acid, the safety profile, overall survival rate and time to first SRE were similar between the treatment groups.