Vascular calcification results from the deposition of calcium phosphate crystals (hydroxyapatite) as a consequence of disordered calcium phosphate regulation in the blood vessel. Hydroxyapatite is secreted in vesicles that bleb out from vascular smooth muscle cells or pericytes in the arterial wall. The mechanism of vascular calcification is not fully understood, but probably involves a phenotypic change in the vascular smooth muscle cells in the wall with activation of bone-forming programs. Numerous regulators of calcification such as osteopontin, osteoprotegerin, matrix gla protein and fetuin-A, receptor activator of NF-kappa-B, receptor activator of NF-kappa-B ligand and tumor necrosis factor (TNF)-related apoptosis-inducing ligand protein have been implicated in this process.