The relationship between calcium intake and bone mass remains controversial. In this paper, the published research on this association is reviewed using the quantitative technique of meta-analysis. Selection of studies was based on defined eligibility criteria, and information relating to study design was recorded. Study results were converted, where necessary, to similar outcome measures so that direct comparison among studies was possible. A total of 37 eligible papers, representing 49 separate studies or parts of studies, were identified in the literature. Calcium had a consistent prevention effect on the rate of bone loss in the 12 studies of calcium supplements in postmenopausal women. This effect was greatest in studies in which the baseline calcium was low, supporting the idea of a threshold beyond which the effect of calcium is reduced. Cross-sectional studies showed a small but consistent positive correlation between calcium intake and bone mass. This association was greater in studies of premenopausal women. Some caution is needed in interpreting the results of this meta-analysis because of the poor quality of many of the studies reviewed. Nevertheless, the consistency of findings suggests that women in their early postmenopausal years will benefit from a high calcium intake.