In terms of both exogenous sources (diet), and endogenous production (activation through exposure to ultraviolet light), vitamin D is unique. Few foods naturally contain vitamin D and only a few are fortified with vitamin D. Most people get more than 90% of their vitamin D requirements from exposure to sunlight. Those who protect their skin from ultraviolet-B radiation with clothing or sunscreen, the elderly, and dark-skinned individuals have limited capacity to produce vitamin D. Vitamin D deficiency is common in the general population and even more common in patients with chronic renal failure (CKD). Increased use of sun-blocking agents and decreased exposure to sunlight, to reduce the risk of skin cancer, attributed to exposure to UV radiation, may contribute to the increase in vitamin D deficiency in the population. These issues are particularly important in the dialysis population who are at particular risk because these, mostly elderly, individuals have an inactive life style and have reduced exposure to sunshine and UV light, thus limiting the actinic synthesis of vitamin D. The nephrology community seems to have overlooked the importance of vitamin D for overall health and well being in patients with CKD. Recently however, several authors have called attention to the role of plasma 25(OH)D-3 levels in mineral metabolism dysregulation in patients with chronic kidney diseases, and those on dialysis. Vitamin D not only contributes to skeletal health but also plays a major role in the health of a wide variety of other organ systems. It seems that vitamin D supplementation is the most effective way of preventing vitamin D deficiency.