Recently, safety concerns about calcium supplementation have arisen. In this situation, ensuring appropriateness of use is highly important. We aimed to describe the use of calcium and vitamin D supplements, the factors related to it, and to assess the appropriateness of calcium prescription among men and women aged 50 years or older. We performed a cross-sectional study in 2009–2010 including 11,035 adults who belong to the ESOSVAL cohort and attend 272 primary healthcare centers in the Valencia region of Spain. Criteria for the inappropriateness of calcium prescription, based on guidelines and recent evidence, were: excessive or insufficient daily total intake (diet plus supplements), excessive single doses of supplements, excessive or insufficient association with vitamin D, and overall inappropriateness. Calcium and/or vitamin D were prescribed to about 17% of the population. Older age, antiosteoporotic treatment, use of glucocorticoids, and a diagnosis of osteoporosis were related to prescription. The presence of other secondary causes of osteoporosis determined supplementation only in men. Calcium dietary intake was not related to the prescription of supplements. Among calcium users, 85.8% met at least one criterion of inappropriate prescription; 29% had an inappropriate daily total intake mainly resulting from excessive consumption (>2000 mg/day); 53.8% of patients were given calcium supplements in quantities higher than 500 mg per dose; and 38.9% of individuals receiving calcium supplements had inappropriate (absent or below 800 UI/day) vitamin D supplementation (all of them at high risk). In conclusion, we found high inappropriateness of calcium supplementation, mainly because of calcium overdosing, and also to undertreatment and underdosing of vitamin D in high-risk patients. Physicians should be encouraged to assess calcium dietary intakes before supplementation, recommending intake from food whenever possible, and to prescribe low calcium doses and high vitamin D doses when given in fixed-dose combinations, or vitamin D alone when calcium is not necessary. © 2013 American Society for Bone and Mineral Research