One hundred and ninety five patients who underwent successful percutaneous transluminal coronary angioplasty (PTCA) for single vessel disease and have been followed up for more than 6 months are being reported. Angiography was done routinely in first 20 patients (Group 1) 8 to 15 weeks (mean 9.6 weeks) after PTCA. Restenosis (loss of 50% of the initial improvement in luminal diameter) was seen in 4 patients (20%). The remaining 175 patients (Group II) have been followed up clinically and subjected to serial exercise testing. Coronary angiography was performed only if symptoms and/or objective evidence of ischemia recurred. In this group, restenosis suspected clinically and confirmed by angiography occurred in 37 patients (21%), 2 to 23 weeks (mean 12.5 weeks) after PTCA. The restenosis rate for the entire patient population was 21%. In general the restenosed lesions were longer and tighter than the lesions before PTCA. A comparison of 41 patients with restenosis with those who did not have clinical restenosis revealed a proximal left anterior descending artery (LAD) involvement (66% vs 31%, p = 0.01), crescendo unstable angina (37% vs 16% p = 0.05), length of pre PTCA stenotic lesion greater than or equal to 1 cm (41% vs 27.5%, p less than 0.05), absence of intimal haziness in immediate post PTCA angiogram (27% vs 16%, p less than 0.05) and residual stenosis greater than or equal to 25%, (34% vs 14% p less than 0.05) in the restenosis group. Repeat PTCA was done in 30 patients with a 96% success rate; 4 patients required coronary artery bypass grafting (CABG). Restenosis after PTCA is a significant problem in our experience.(ABSTRACT TRUNCATED AT 250 WORDS)