Background:After acute coronary syndrome (ACS), there is a high risk of recurrent cardiovascular events. Triglyceride-rich lipoproteins influence residual cardiovascular risk in patients taking statin. This study examined the predictive value of remnant lipoprotein level for secondary cardiovascular events in patients treated with statins after ACS.Methods and Results:A total of 190 patients treated with statins after ACS were enrolled in the study. The serum level of remnant lipoproteins (remnant-like lipoprotein particle cholesterol; RLP-C) was measured using an immunoseparation method. All the patients were followed prospectively for a maximum period of 70 months or until the occurrence of one of the following events: cardiac death, non-fatal myocardial infarction, unstable angina requiring unplanned coronary revascularization, or ischemic stroke. During the follow-up period, 42 patients had a secondary event. Multivariate Cox analysis showed that a high level of RLP-C (≥5.4 mg/dl; determined on receiver operating characteristic curve analysis) was a significant risk factor for secondary events, independent of conventional risk factors (hazard ratio, 2.94; 95% confidence interval: 1.40–6.18; P<0.01). The addition of high RLP-C to traditional risk factors enhanced net reclassification improvement (NRI) and integrated discrimination improvement (IDI) (NRI, 0.66, P=0.0003; and IDI, 0.08, P=0.0002).Conclusions:RLP-C is useful for risk assessment of secondary cardiovascular events in patients treated with statins after ACS. (Circ J 2014; 78: 2492–2500)