Coronary occlusion or myocardial infarction occurred in 50 of 394 (13%) one-vessel-disease patients awaiting percutaneous transluminal coronary angioplasty (PTCA). To identify risk factors for these events, we first matched the 37 patients who demonstrated occlusion on the immediate preangioplasty repeat angiogram with 37 patients who did not. Matching was based on the time interval between angiograms, the date of the procedure, and the site of the lesion. Preangioplasty occlusion patients did differ from controls by age (47 +/- 11 vs 54 +/- 8 years, P less than .01), smoking status (34/37 vs 24/37, P less than .01), and angina class (2.6 +/- 1.0 vs 2.3 +/- 0.7, P less than .10) at the time of the first angiogram. Second, we pooled the data of the 37 preangioplasty occlusion patients with those of the 13 patients with preangioplasty myocardial infarction. The 50 cases with complication (coronary occlusion or myocardial infarction) were younger (47 +/- 12 vs 54 +/- 8 years, P less than .01), more often smokers (42/50 vs 24/37, P less than .05), and more symptomatic (2.7 +/- 0.8 vs 2.3 +/- 0.7, P less than .05) than the 37 controls. This study suggests that young smokers with severe angina are at high risk of preangioplasty occlusion and/or myocardial infarction; prompt management of these patients, when considered for PTCA, seems advisable.