Long-term vitamin D and calcium supplementation is effective in reducing nonvertebral fractures in elderly people. Increased bone fragility caused by secondary hyperparathyroidism (sHPT) and impaired balance are known risk factors for hip fractures. The hypothesis is that short-term therapy with calcium and vitamin D may improve body sway as well as sHPT more effectively than calcium monotherapy. The effects of 8 weeks of supplementation with vitamin D (cholecalciferol) and calcium on body sway and biochemical measures of bone metabolism were measured. The sample consisted of 148 women (mean [+/-SD] age, 74 +/- 1 years) with a 25-hydroxycholecalciferol level below 50 nmol/liter. They received either 1200 mg of calcium plus 800 IU of vitamin D or 1200 mg of calcium per day. We measured intact parathyroid hormone (PTH), markers of bone turnover, and body sway before and after treatment. Falls and fractures among the participants were followed over a 1-year period. Compared with calcium mono, supplementation with vitamin D and calcium resulted in an increase in serum 25-hydroxyvitamin D of 72% (p < 0.0001), a decrease in the serum PTH of 18% ( p = 0.0432), and a decrease in body sway of 9% (p = 0.0435). The mean number of falls per subject during a 1-year follow-up period was 0.45 for the calcium mono group and 0.24 for the calcium and vitamin D group (p = 0.0346). Short-term supplementation with vitamin D and calcium improves sHPT and body sway and therefore may prevent falls and subsequent nonvertebral fractures in elderly women.