Vitamin D deficiency is a major risk factor for accelerated bone loss, which contributes to morbidity in older adults. It is easy to diagnose, and treatment is safe and cost-effective. This article reviews the amount of vitamin D needed by certain populations in order to help prevent osteoporosis and fractures associated with the disease. It also summarizes the results of a study involving 81 hip-fracture patients that found 80% had abnormally low levels of 25-hydroxyvitamin D.