Calcium supplementation is widely used for the prevention of osteoporosis in postmenopausal women and in men. While there has been ongoing debate regarding its effectiveness in fracture prevention, the underlying assumption has been that, even if it was not particularly effective, at least it was safe. The recent finding of the Auckland Calcium Study that myocardial infarctions were more common in women randomised to calcium calls this assumption into question, and consideration of vascular event data from other calcium trials does not refute the Auckland findings. Meta-analyses of these data will be necessary to settle this matter. It is already accepted that calcium supplements increase vascular risk in patients with renal compromise, even in those not yet requiring dialysis. Also, there is substantial epidemiological evidence that serum calcium levels in the upper part of the normal range are a risk factor for vascular disease, and that calcium supplements acutely elevate serum calcium - a combination of findings that lends plausibility to supplementation increasing vascular risk. As there are reasonable grounds for doubting the safety of calcium supplements, and as the evidence for their efficacy in fracture prevention remains marginal, we suggest that there should be a reappraisal of their role in the management of osteoporosis, with a greater emphasis on agents known to prevent fractures.