The effect of immediate recoil on the results of balloon angioplasty was examined in a group of 416 patients (596 lesions) who underwent successful coronary angioplasty. Immediate recoil was responsible for loss of 0.42 +/- 0.64 mm from the potentially achievable lesion diameter, and represented 23% of the actual gain in diameter. The immediate recoil was determined mainly by the degree of arterial stretch, which is best represented by the balloon to normal artery size ratio (correlation coefficient 0.49, p < 0.0001). Classic risk factors for coronary artery disease did not affect immediate recoil, except for a trend toward lower values in patients with history of hypercholesterolemia. There was a tendency for lower recoil in patients with residual coronary thrombus and in those who underwent angioplasty within 1 week of acute myocardial infarction. Recoil was larger in the left anterior descending artery than in the circumflex or the right coronary artery. Patients with more immediate recoil developed more restenosis (> 50% stenosis at follow-up). However the late loss of luminal diameter due to the restenotic process was smaller in those who had larger initial recoil. It is concluded that immediate recoil after balloon angioplasty is an elastic phenomenon that is related mainly to the degree of arterial stretch. The relative importance of immediate recoil in determining the late outcome of coronary angioplasty is at least as important as the late restenotic process.