One hundred and fifty patients with coronary artery disease (CAD), 14 (9.3%) of whom had coexisting peripheral vascular disease, underwent bilateral internal mammary arteriography to study the incidence and extent of atherosclerosis in these vessels. Significant atherosclerosis of the internal mammary arteries (IMAs) was present in three patients (2%), of whom one had coexisting peripheral vascular disease. Lesions in the IMAs were found either proximally, close to the origin or distally, around the terminal bifurcation. Six of the 14 patients with peripheral vascular disease (4% of total subjects) had significant atherosclerosis of the brachiocephalic arteries. Atherosclerotic involvement of the IMA is very unusual and rarely interferes with the use of these vessels for coronary bypass. More common, however, is atherosclerosis of the subclavian arteries, a contraindication for IMA grafting if the lesion is proximal to the IMA origin.