Vitamin D (cholecalciferol) is important for normal development and maintenance of the skeleton. The metabolites 25(OH)D and 1,25(OH)(2)D are not only important for treating rickets and osteomalacia but also for all types and clinical stages of osteoporosis. Patients with low calcium intake and a low vitamin D status are at risk to develop secondary hyperparathyroidism, increased bone resorbtion, osteopenia and fractures. This can be counteracted by a lifelong sufficient vitamin D supply plus dietary or supplementary calcium. The effects of vitamin D on muscle, balance and cognitive functions may be an added value in fracture prevention. Today it is generally accepted that a supplementation with vitamin D and calcium should be added to every specific medical treatment of osteoporosis. In contrast to this general recommendation the potency of vitamin D alone with or without calcium to reduce the incidence of falls and/or fractures is still a debated controversy. Studies and meta-analyses during the last two decades on the effect of vitamin D and calcium supplements have not resolved the controversy on the risk of falls and fractures in healthy or osteopenic elderly populations. A thorough analysis of these trials supports our clinical experience that the efficacy of vitamin D-calcium supplementation depends on factors related to patient selection, medical intervention and study design, e.g. age, mobility, preventing falls and fractures, co-morbidity, initial vitamin D status and renal function. We conclude that plain vitamin D (cholecalciferol) with sufficient calcium intake is able to reduce the risk of falls and fractures only when adopting optimal selection criteria for patients and study conditions.