['To assess the cost implications for a preventive treatment strategy for institutionalised elderly women with a combined 1200 mg/day calcium and 800 IU/day vitamin D(3) supplementation in seven European countries.', 'Retrospective cost effectiveness analysis based on a prospective placebo-controlled randomised clinical trial.', 'Recently published cost studies in seven European countries. Clinical results from Decalyos, a 3-year placebo-controlled study in elderly institutionalised women.', 'Decalyos study, with 36 months follow-up of 3270 mobile elderly women living in 180 nursing homes, allocated to two groups. One group received 1200 mg/day elemental calcium in the form of tricalcium phosphate together with 800 IU/day (20 microg) of cholecalciferol (vitamin D(3)), the other placebo.', 'In the 36 months analysis of the Decalyos study, 138 hip fractures occurred in the group of 1176 women, receiving supplementation and 184 hip fractures in the placebo group of 1127 women. The mean duration of treatment was 625.4 days. Adjusted to 1000 women, 46 hip fractures were avoided by the calcium and vitamin D(3) supplementation. For all countries, the total costs in the placebo group were higher than in the group receiving supplementation, resulting in a net benefit of 79000-711000 per 1000 women.'] Is calcium-vitamin D3 supplementation cost-effective in hip fractures prevention?