Background We aimed to investigate the determinants and outcomes of multiple complex lesions (MCLs) on coronary angiography in patients with an acute myocardial infarction. Methods One thousand one hundred fifty-two consecutive nonselected myocardial infarction patients who underwent coronary angiography within 24 hours after admission were analyzed. A complex lesion was defined by the presence of thrombus, ulceration, irregular plaque, and flow impairment. Patients with ≤1 complex lesion were considered with single complex lesion (SCL), and patients with >1 complex lesions with MCLs. Results Multiple complex lesions were identified in 360 patients (31%). Patients from the MCL group were older and had a higher rate of cardiovascular risk factors but were less likely to be smokers when compared with the SCL group. Patients with MCLs were more likely to have altered left ventricular ejection fraction and multivessel disease and showed a trend toward an increased median time delay to revascularization (360 vs 285 minutes; P = .070). Moreover, the C-reactive protein (CRP) plasma levels increased with the number of CLs. By multivariate analysis, multivessel disease and CRP level were associated with the presence of MCLs. When compared with the SCL group, patients with MCLs had a higher risk of inhospital cardiogenic shock (18% vs 11%; P = .005) and 30-day mortality (11% vs 6%; P = .002). At 1-year follow-up, the presence of MCLs was an independent predictive factor of death. Conclusions This study shows that the presence of MCLs is associated with worse outcomes and that risk factors such as CRP are able to identify patients at a high risk for MCLs.