To assess the possible progression of coronary artery disease after percutaneous transluminal coronary angioplasty (PTCA) and its relation to risk factors and restenosis, 124 patients who underwent a first successful PTCA were studied. All had routine follow-up angiography 5 to 8 months after PTCA. Restenosis was defined as a 30% decrease in diameter stenosis or a return to greater than 50% stenosis, and progression (in any nondilated site) as a 20% decrease in diameter stenosis, assessed by a video-densitometric computer-assisted technique. Univariate and multivariate analysis with respect to progression was carried out for age, sex, initial unstable angina, previous myocardial infarction, diabetes mellitus, hypertension, hypercholesterolemia (greater than or equal to 6.2 mmol), smoking habits, Jenkins' score, dilated artery and restenosis. Forty-one patients (33%) had restenosis, and 23 (19%) had evidence of progression; 20 (87%) of these latter patients had restenosis and 3 (13%) did not. Univariate correlates of progression were: previous myocardial infarction (p less than 0.05), higher Jenkins' score (p less than 0.0003) and restenosis (p less than 0.0001). Restenosis was the only multivariate correlate (p less than 0.00003). Progression at routine angiography after PTCA is not rare, and appears to be related to both the initial extent of coronary artery disease and restenosis.