117 postmenopausal women who were enrolled in the HORIZON trial were recruited for this ancillary study which investigated the effect zoledronate (ZOL) on bone mineral density (BMD) of the tibia. This study measured tibial epiphsyis and tibial diaphysis BMD at 12, 24, and 36 months, and compared results to a group treated with placebo (PBL group). Results on tibial epiphysis BMD indicated an increase in the ZOL group and decrease in the PLB group throughout follow-up compared to baseline values, with statistically significant difference between groups at all time points. No significant differences in tibial diaphysis BMD were observed throughout the study.