With the increasing use of the internal mammary artery as the conduit of choice in coronary bypass surgery, it is anticipated that an expanding patient population will have stenosis, usually at the site of internal mammary-to-coronary artery anastomosis. In our series 31 patients underwent dilatation at either the site of anastomosis (24), the native coronary artery beyond the anastomosis (4), or both (3) with no mortality, myocardial infarction, or need for emergency coronary artery bypass surgery. Angiographic and clinical success was achieved in 28 patients (90%). There were two internal mammary artery dissections with both patients requiring elective coronary bypass surgery. Of the patients in whom dilatation was successful, 22 (79%) have been followed for longer than 6 months and 19 (86%) have had sustained functional improvement at a mean of 35 months after angioplasty. One patient is to undergo repeat coronary bypass surgery. No patient has had a myocardial infarction or died during follow-up. Although percutaneous transluminal coronary angioplasty of the internal mammary artery has inherent difficulties because of the anatomic characteristics of the vessel, it can be performed with a high degree of primary success and a low incidence of complications and can provide long-term clinical improvement.