Summary: Alfacalcidol (1alpha-OH-cholecalciferol) is a synthetic calcitriol precursor which is rapidly converted in the liver to calcitriol following oral or parenteral administration. Its clinical indications include secondary hyperparathyroidism and osteodystrophy in adults with chronic renal failure, hypoparathyroidism, vitamin D-resistant rickets, and osteomalacia, and in selected cases of osteoporosis. In the first part of the article, we summarize the metabolism and role of vitamin D in human physiology, the pathogenesis and clinical consequences of hyperparathyroidism secondary to chronic kidney disease, and the place of alfacalcidol in its treatment. In the second part, we briefly discuss the use of alfacalcidol in hypoparathyroidism.