OBJECTIVE--To estimate the initial outcome and incidence of restenosis of angioplasty of internal mammary artery grafts in a retrospective study. METHODS--The study population consisted of 46 patients (48 lesions) who underwent first balloon angioplasty within the internal mammary artery graft. Most (37/48) were at the distal anastomosis. A few (8/48) were in the graft body. Six patients with the evidence of angiographic restenosis underwent a second angioplasty. RESULTS--The success rate and the restenosis rate of the first angioplasty was 73% and 30% respectively. Of the 34 patients (35 lesions) with a successful first angioplasty, 30 underwent follow up angiography with a restenosis rate of 30% (9/30). A second angioplasty was performed on six of the nine restenotic lesions, with a success rate of 83% and no restenoses. The percent diameter stenosis of the recipient native coronary artery was significantly greater in the restenosis group, at 75 (SD 27)% v 89 (17)%, p < 0.05. CONCLUSIONS--First angioplasty of 46 patients (48 lesions) within an internal mammary artery graft was performed with a success rate of 73% and a restenosis rate of 30% (follow up rate of 88%). The extent of the stenosis of the recipient native coronary artery may affect the restenosis rate.