Use of single internal mammary artery grafts in older patients. The indications for use of the internal mammary artery as a coronary bypass conduit in older patients are not clearly established. Between January 1985 and December 1988, 786 patients received single internal mammary artery grafts alone (717) or in conjunction with other procedures (69). Of these patients, 341 were 65 years of age or older (mean, 69.3 years). This group was compared with those patients less than 65 years of age (mean, 56.2 years). There were no significant differences between the two groups in the incidence of diabetes mellitus; the number of distal coronary anastomoses; left ventricular wall motion score; the frequency of isolated bypass procedures, reoperations, or emergent operations; or the durations of aortic clamping and cardiopulmonary bypass. The older group contained more women (34.9% versus 20.7%) and more patients with left main coronary artery disease (15.5% versus 9.4%) (p less than 0.01). No significant differences in the frequency of reoperation for hemorrhage, perioperative infarction, neurological deficits, requirements for intra-aortic balloon pumping, sternal wound infections, necessity for prolonged ventilatory support, or 30-day mortality (2.7% versus 3.2%) were observed. The length of postoperative hospitalization was greater in the older group (11.8 versus 10.2 days) (p = 0.02). Blinded histological examination of biopsies from 61 internal mammary artery grafts (34 patients less than 65 years, 27 patients greater than or equal to 65 years) showed no significant differences in luminal area or wall thickness. No significant degenerative changes were observed in either group. We conclude that the use of the internal mammary artery for bypass grafting in older patients is safe and may provide long-term benefit. 