The effects of a vertical jumping exercise regime on bone mineral density (BMD) have been assessed using randomized controlled trials in both pre- and postmenopausal women, the latter stratified for hormone replacement therapy (HRT). Women were screened for contraindications or medication likely to influence bone. The premenopausal women were at least 12 months postpartum and not lactating; the postmenopausal women had been stable on, or off, HRT for the previous 12 months and throughout the study. BMD was measured blind using dual-energy X-ray absorptiometry at the spine (L2-L4) and the proximal femur. The exercise consisted of 50 vertical jumps on 6 days/week of mean height 8.5 cm, which produced mean ground reactions of 3.0 times body weight in the young women and 4.0 times in the older women. In the premenopausal women, the exercise resulted in a significant increase of 2.8% in femoral BMD after 5 months (p < 0.001, n = 31). This change was significantly greater (p < 0.05) than that found in the control group (n = 26). In the postmenopausal women, there was no significant difference between the exercise and control groups after 12 months (total n = 123) nor after 18 months (total n = 38). HRT status did not affect this outcome, at least up to 12 months. It appears that premenopausal women respond positively to this brief high-impact exercise but postmenopausal women do not.