OBJECTIVES: To determine whether vitamin D supplementation can reduce the incidence of falls and fractures in older people in residential care who are not classically vitamin D deficient. DESIGN: Randomized, placebo-controlled double-blind, trial of 2 years' duration. SETTING: Multicenter study in 60 hostels (assisted living facilities) and 89 nursing homes across Australia. PARTICIPANTS: Six hundred twenty-five residents (mean age 83.4) with serum 25-hydroxyvitamin D levels between 25 and 90 nmol/L. INTERVENTION: Vitamin D supplementation (ergocalciferol, initially 10,000 IU given once weekly and then 1,000 IU daily) or placebo for 2 years. All subjects received 600 mg of elemental calcium daily as calcium carbonate. MEASUREMENTS: Falls and fractures recorded prospectively in study diaries by care staff. RESULTS: The vitamin D and placebo groups had similar baseline characteristics. In intention-to-treat analysis, the incident rate ratio for falling was 0.73 (95% confidence interval (CI)=0.57-0.95). The odds ratio for ever falling was 0.82 (95% CI=0.59-1.12) and for ever fracturing was 0.69 (95% CI=0.40-1.18). An a priori subgroup analysis of subjects who took at least half the prescribed capsules (n=540), demonstrated an incident rate ratio for falls of 0.63 (95% CI=0.48-0.82), an odds ratio (OR) for ever falling of 0.70 (95% CI=0.50-0.99), and an OR for ever fracturing of 0.68 (95% CI=0.38-1.22). CONCLUSION: Older people in residential care can reduce their incidence of falls if they take a vitamin D supplement for 2 years even if they are not initially classically vitamin D deficient.