Vitamin D deficiency is extremely prevalent in the elderly. Most often the first symptoms are caused by myopathy with muscle pain, fatigue, muscular weakness and gait disturbances. More severe deficiency causes osteomalacia with deep bone pain, reduced mineralization of bone matrix and low energy fractures. Recent data also suggest that hypovitaminosis D increases the risk of cancer of the prostate, colon and breast. Thus, hypovitaminosis D is associated with many diseases associated with aging. In order to diagnose hypovitaminosis D, the assessment of serum levels of 25-hydroxy vitamin D is mandatory. Screening based on other markers like alkaline phosphatase and parathyroid hormone (PTH) will be incomplete. The treatment of hypovitaminosis D is simple with administration of combined calcium (I g) and vitamin D supplements (calciferol, at least 800 IU). Severe cases may demand initial parenteral administration of vitamin D (repeated injections of 300,000 IU 2-3 times with monthly intervals). More potent analogues are rarely needed. One should aim at achieving S-25(OH)D values in the range 50-100 nmol/l.