Among 3,548 patients undergoing a percutaneous transluminal coronary angioplasty procedure, 714 had multilesion angioplasty (1,550 lesions) in a single session. Acute occlusion occurred in 22 patients (3.1%) and 29 lesions (1.9%). The patients were classified into a group undergoing multivessel angioplasty (348 patients, 785 lesions) and a group undergoing multilesion single vessel angioplasty (366 patients, 765 lesions). The rate of acute occlusion was similar in both patient groups. The multivessel angioplasty group had a 2.9% rate per patient (n = 10) and a 1.7% rate per vessel; the multilesion single vessel group had a 3.3% rate per patient (n = 12) and a 2.1% rate per lesion. Five of the 10 patients from the multivessel group with acute occlusion, but only 1 of the 12 patients with occlusion in the single vessel multilesion group, required emergency open heart surgery. No patient in either group died as a consequence of coronary angioplasty. Occlusion occurred during angioplasty in 15 of the 22 patients, and 1 to 24 h after angioplasty in 7 of 22 patients. In the group with multivessel angioplasty, acute occlusion during the procedure was mainly linked with hypotension during the second vessel dilation, whereas in this group with delayed vessel closure and in the multilesion single vessel group, existence of intimal tearing constituted the most important factor for acute occlusion (12 of 16 patients). Closure of vessel per major coronary system was evenly distributed in the multivessel group, whereas significantly more left circumflex vessels closed in the single vessel multilesion group (6.1% versus 1.3% in the left anterior descending coronary artery and 1.1% in the right coronary artery; p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)