Control angiographic studies were carried out 54 to 88 months after aortocoronary saphenous vein bypass surgery (70 +/- 10 months) in 100 unselected patients who were known to have at least one patent graft 6 to 18 months following the operation. Only 17 of the 159 grafts were found occluded during this interval of 5 years, giving an average yearly attrition rate of 2.1% after the first year. The mean yearly attrition rate was 0.7% in our second series of near consecutive patients operated on after 2 years of experience and modifications of surgical techniques, and it compares favorably with the 2.4% yearly attrition rate found in our first series of patients (P < 0.05). Of the 37 grafts having localized stenoses at 1 year, eight became occluded (21.6%), and four became worse. Grafts with localized stenoses were more prone to late occlusion, whereas no late occlusion was observed in normally appearing grafts at 1 year. Diffuse graft narrowing noted during the first year showed no further change during the subsequent 5 years, and it did not appear to lead to late occlusion. Finally, in 14 grafts, localized narrowing developed after the first year, at a yearly rate of 1.5%. Atherosclerosis appears to be the most likely etiology, being found in two of these instances at reoperation.