An increase in the thickness of the lining of a blood vessel in response to injury or vascular reconstruction. It is an important cause of vein graft obstruction after coronary artery bypass surgery and in the premature closure of other vascular conduits (e.g., in dialysis access devices). It is characterized by the migration of smooth muscle cells into the graft, followed by the release of cytokines that damage the vessel wall and contribute to its degradation by inflammation.