A total of 1,179 vein grafts were studied angiographically in 353 (45%) unselected survivors (male, mean age 45.5 years) of 786 coronary bypass operations. Studies were conducted early (0.96 months), 1 year (12.8 months), and 5 years (59.7 months) postoperatively. A previously described technique was used to grade the patency of the grafts, and a new technique was used to assess intimal irregularity, presumably caused by atherosclerosis; this new technique indicated both intimal surface distribution of disease and profile (relief or elevation). Ten percent, 17%, and 26% of grafts were occluded early, at 1 year, and at 5 years, respectively. Distal anastomotic defects were the commonest cause for low grades in the patency classification. Irregularities in patent grafts increased from 9% at 1 year to 42% at 5 years, with 11% of all the 1 year lesions and 20% of all the 5 year lesions having a high profile (more than 50% graft stenosis); of the lesions categorized as showing the widest surface spread, 17% were in high relief at 1 year and 34% at 5 years. Thus, the lesions we believed to be atherosclerotic proliferated in both surface spread and elevation. All severely diseased grafts at the 1 year study had been normal in outline early; 79% at the 5 year study had been disease free at 1 year. All newly occluded grafts at the 1 year study had been normal in outline and 82% had had good patency early; 78% of newly occluded grafts at the 5 year study had been disease free at 1 year and 77% had had good patency. Normal appearance of the intima in grafts studied at 1 year had no prognostic value for 5 year findings. However, 62% of all grafts with the appearance of intimal disease at 1 year showed deterioration by 5 years, and 28% were occluded. The differences between these outcomes are highly significant (p less than 0.0005). In conclusion, the appearance of intimal irregularity compatible with atherosclerosis in a coronary bypass graft 1 year after operation carried a poor prognosis for adverse angiographic change at 5 years. On the other hand, normally appearing intima at 1 year had no predictive valve for the 5 year study despite a generally better prognosis for nondiseased grafts.