OBJECTIVES: To determine the prevalence of vitamin D deficiency in older people in residential care and the influence that the level of vitamin D may have on their incidence of falls.DESIGN: Prospective cohort.SETTING: Residential care facilities for older people in several states of Australia.PARTICIPANTS: Six hundred sixty-seven women in low-level care and 952 women in high-level care, mean age 83.7 years.MEASUREMENTS: Serum 25-hydroxyvitamin D (25D) levels and recognized risk factors for falls including current medication use, a history of previous fractures, weight, tibial length (as a surrogate for height), cognitive function, walking ability, and frequency of going outdoors were determined. The women in low-level care and high-level care were followed for an average of 145 and 168 days, respectively. Falls were recorded prospectively in diaries completed monthly by residential care staff.RESULTS: Vitamin D deficiency (defined as a serum 25D level below 25 nmol/L) was present in 144 (22%) women in low-level care and 428 (45%) in high-level care. After excluding 358 bed-bound residents and adjusting for weight, cognitive status, psychotropic drug use, previous Colles fracture, and the presence of wandering behavior, log serum 25D level remained independently associated with time to first fall. The adjusted hazards ratio was 0.74 (95% confidence interval=0.59-0.94; P=.01), implying a 20% reduction in the risk of falling with a doubling of the vitamin D level.CONCLUSION: Vitamin D deficiency is common in residential care in Australia. A low level of serum vitamin D is an independent predictor of incident falls.