We have correlated the location of early atheroma with vessel geometry in the major coronary arteries of subjects dying of noncardiovascular causes under 40 yr of age. We analyzed only those vessels affected minimally by very early (fatty) disease. In each of the three major branches, disease was concentrated close to the entrance and diminished with distance downstream. Circumferential distribution of disease was also not random. In the right coronary artery, lesions were concentrated on the inner wall of the major curvature. Immediately downstream of the entrances of both branches of the left coronary artery, the flow-dividing walls were spared. Further downstream in the left anterior, descending branch plaques followed a spiral distribution. We believe these patterns may be determined by local mechanical factors.