Percutaneous transluminal coronary angioplasty (PTCA) is increasingly performed in patients with multivessel coronary artery disease (CAD) despite reports showing relatively low rates of complete revascularization and poorer long-term prognosis for patients with significant residual narrowings. Reasons for incomplete revascularization were assessed in 618 patients with multivessel CAD in the 1985-1986 National Heart, Lung, and Blood Institute (NHLBI) PTCA Registry. The PTCA operator was asked to describe the treatment plan and outcome for each of the 1,942 significant lesions (greater than or equal to 50% luminal diameter stenosis) in the Registry patients. Although all significant narrowings were considered amenable to balloon angioplasty in 77% of patients, complete correction was intended only for 34% of them. It was attempted in 28% and successful in 19%. Only 63% of total occlusions were considered amenable to PTCA and only 54% of those attempted were successfully dilated. PTCA was intended for 38% with 50 to 69% stenoses versus 80% with 70 to 89% stenoses and for greater than 85% with narrowings greater than or equal to 90%. Dilatation in narrowings of the left circumflex and left anterior descending artery systems was intended less frequently than in lesions of the right coronary artery. Finally, there was wide variability in operator strategy among the different Registry sites.(ABSTRACT TRUNCATED AT 250 WORDS)