A disruption in any part of the vitamin D physiological pathway can result in vitamin D deficiency, which may lead to bone pain, muscle weakness, falls, low bone mass, and fractures. Recognizing the signs and symptoms helps physicians make a proper diagnosis and prescribe appropriate treatment. Physicians should suspect osteomalacia in patients who have prolonged vitamin D deficiency, a low serum calcium level, or a low serum phosphorus level. Patients with cystic fibrosis are at increased risk for deficiencies in fat-soluble vitamins, including vitamin D. Secondary hyperparathyroidism can develop in patients with chronic kidney disease as a result of low 25-hydroxyvitamin D levels or impaired conversion to 1,25-dihydroxyvitamin D. Patients may experience abnormal vitamin D metabolism as a result of taking anticonvulsants and other medications.