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 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 hr after the onset of symptoms were divided into three groups: early reperfusion (ER; <- 12 hr, n = 1,647), late reperfusion (LR; > 12 hr, n = 219), and failed reperfusion (RF; n = 343). We evaluated the incidence, risk ratio, and predictors of mechanical complication. 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 LR group [risk ratio 7.34, 95% confidence interval (CI) 1.02 - 52.80, p = 0.04]. Predictors of an increased risk of mechanical complications by multivariate analysis were age >- 70 years (odds ratio 3.68, 95% CI 1.56-8.64, p < 0.01), Killip class >- II (odds ratio 3.73, 95% CI 1.52-9.12, p >- 0.01), absence of collateral vessels (odds ratio 4.09, 95% CI 1.17-14.26, p = 0.03), and FR (odds ratio 2.68, 95% CI 1.01-6.61, p = 0.03). In conclusion, successful late reperfusion by primary coronary angioplasty is associated with the reduced risk of mechanical complications in patients with acute myocardial infarction.