Calcium supplementation has long been regarded as a fundamental part of the prevention and treatment of postmenopausal bone loss. A number of other health benefits have been suggested, including improvements in blood pressure and in serum cholesterol profiles. In light of this, we recently explored the effects of calcium supplementation on vascular disease in a large, randomized, controlled trial carried out in healthy postmenopausal women over a period of 5 years. To our surprise, we found substantial increases in vascular event rates, particularly myocardial infarction, in women randomized to calcium. These effects were more marked in those who were highly compliant with their calcium supplements. There are similar adverse trends in several other recent studies of calcium supplementation, although these are not statistically significant within each of those trials. Calcium supplementation also appears to accelerate vascular disease in patients with renal impairment, including those not yet requiring dialysis. The recent data do not provide conclusive evidence that calcium has adverse effects on vascular disease, but are consistent enough to mandate that this possibility is considered when providing advice regarding calcium intake. Further research in this area is a high priority on the women's health agenda.