It has been suggested that early treatment decreases, but late treatment increases, the risk of mechanical complications for a thrombolytic strategy. However, few studies have evaluated whether late reperfusion (LR) by primary coronary angioplasty decreases the risk of mechanical complications. A total of 2,209 patients with acute myocardial infarction treated with primary coronary angioplasty within 24 hours after the onset of symptoms were divided into 3 groups: early reperfusion (ER; < or =12 hours, n = 1,647), LR (>12 hours, n = 219), and failed reperfusion (FR; n = 343). We evaluated the incidence, risk ratio, and predictors of mechanical complications. The overall incidence of mechanical complications was 2.0%. The incidence of mechanical complications was highest in the FR group (ER 1.4%, LR 1.8%, FR 5.0%; p <0.01). After adjusting for clinical variables, the risk ratio for mechanical complications increased in the FR group compared with the LR group (risk ratio 7.34, 95% confidence interval [CI] 1.02 to 52.80; p = 0.04). Predictors of an increased risk of mechanical complications by multivariate analysis were age > or =70 years (odds ratio [OR] 3.68, 95% CI 1.56 to 8.64; p <0.01), Killip class > or =II (OR 3.73, 95% CI 1.53 to 9.12; p <0.01), absence of collateral vessels (OR 4.09, 95% CI 1.17 to 14.26; p = 0.03), and FR (OR 2.68, 95% CI 1.09 to 6.61; p = 0.03). In conclusion, successful LR by primary coronary angioplasty is associated with the reduced risk of mechanical complications in patients with acute myocardial infarction.