Coronary artery bypass grafting in pediatric patients provides a unique opportunity to evaluate the characteristics of graft material. Twelve pediatric patients with severe coronary artery involvement secondary to Kawasaki disease underwent coronary artery bypass grafting with internal mammary artery and autologous saphenous vein grafts. Eleven patients were boys and one was a girl; their ages ranged from 5 to 13 years (mean age +/- SD, 8.7 +/- 3.0 years). These 12 patients had 17 internal mammary artery and 11 autologous saphenous vein grafts with a mean value of 2.3 +/- 0.7 grafts per patient. Five patients underwent bilateral internal mammary artery grafting with or without concomitant autologous saphenous vein grafting. There was no mortality, and all patients are leading almost normal lives, although strenuous exercise is still prohibited for some. Biplanar cineangiography was performed before and 1 month after (early postoperative period) coronary artery bypass grafting in all patients and was repeated more than 1 year after (late postoperative period) bypass in eight patients. Changes in graft diameter and graft length were assessed by computer-assisted graphic analysis of 10 internal mammary artery grafts and of seven saphenous vein grafts between the early and late postoperative periods. Patency rates of saphenous vein grafts and of internal mammary artery grafts were 91% and 100%, respectively, at the early postoperative period (p = NS), and 50% and 100%, respectively, at the late postoperative period (p less than 0.05). In addition to the excellent patency of internal mammary artery grafts in the late postoperative period, an in situ internal mammary artery graft was found to have grown 125% in length with 112% body growth (112% body surface area) (r = 0.88, p less than 0.001) and to have enlarged 149% in diameter when the native coronary stenosis was tight. In contrast, the lengths of saphenous vein grafts either failed to change or were slightly decreased at the late postoperative period (p = NS). Growth potential of the internal mammary artery graft provides a new demonstration of the viability and adaptability of this graft. We conclude that the internal mammary artery graft is a "live" conduit with potential for growth and adaptation. This growth potential may be the most important reason for its excellent long-term patency, which suggests that in situ internal mammary artery grafts are the graft of choice for pediatric coronary artery bypass grafting.