Vitamin D deficiency is a problem of considerable magnitude that has reemerged as a major public health issue in the United States and several other developed countries. Vitamin D plays a crucial role in calcium homeostasis in the body. Hypovitaminosis D leads to osteomalacia and increased risk of fractures, especially in the elderly. Preliminary research suggests that vitamin D can prevent certain types of cancer and autoimmune diseases. A recent large study has shown the association between severe hypovitaminosis D and persistent, non-specific musculo-skeletal pain, further suggesting that patients with no apparent cause of pain should be assessed and possibly treated for vitamin D deficiency.