The location of coronary artery narrowings in coronary disease (CAD) is of considerable importance in assessing the mass of myocardium at risk as well as patient prognosis. The detailed distribution of coronary lesions was mapped in 302 patients with CAD who had coronary angiography for chest pain. All identifiable coronary lesions were measured manually and the site and degree of narrowing were stored in a computer-based multisegmental model of the coronary tree. A high prevalence of CAD was found in proximal vessels and especially at, or adjacent to, proximal points of branching. In the left anterior descending coronary artery, the lesions were most prevalent immediately after the first diagonal branch and at the origin of this branch. In the right coronary artery, there was a high prevalence of narrowing between the infundibular and acute marginal branches and specifically around the origin of the right ventricular branch. In the left circumflex coronary artery, there was a predilection for narrowing in and around the origin of the first marginal branch. When a ramus intermedius was present, its origin was frequently the site of narrowing.