Vitamin D is required for adequate calcium and phosphate metabolism, maintenance of bone structure, and maximum muscle function. Older adults, however, are at risk of inadequate vitamin D levels due to decreased skin synthesis, decreased metabolism in the kidneys, decreased gut absorption, and comorbid medical conditions. A person’s vitamin D status is assessed by measuring the blood level of ... [Show full abstract] 25-hydroxyvitamin D. There is no generally accepted criterion for vitamin D deficiency and insufficiency. Serum 25OHD thresholds <25 nmol/l is defined as deficient, 25–50 nmol/l as insufficient, and >50 nmol/l as adequate for vitamin D. Vitamin D3 is recommended as the vitamin D preparation of choice for the treatment of vitamin D deficiency. Oral administration of vitamin D is recommended over intramuscular administration. A guideline for the treatment of vitamin D deficiency and insufficiency in older adults has been suggested. Compliance to prescribed medications is also a major factor for consideration in older adults. Individualized vitamin D therapy focusing on knowledge of the elderly and/or their carers about their medications and health may help improve adherence.