Background The goal of the present study was to identify predictors of event-free survival in nonischemic dilated cardiomyopathy (NIDCM) patients after administration of angiotensin-converting enzyme inhibitors (ACEI)/angiotensin receptor blockers (ARB) and β-blockers. Methods and Results The study group comprised 78 consecutive patients with NIDCM between 1997 and 2002. NIDCM was defined as ejection fraction (EF) <0.40 and left ventricular end-diastolic diameter (LVEDD) >55 mm on echocardiography and normal coronary angiography. The mean EF and LVEDD was 26.3±10.5%, and 62.9±7.1 mm, respectively. Patients were treated with optimal medical therapy including ACEI/ARBs and/or β-blockers and followed up for 35.6±27.8 months. The primary endpoint was either cardiac death or hospitalization because of deterioration of heart failure. Cox's regression analysis was used to establish the association of age, sex, EF, LVEDD, left atrial diameter, cardiac index, pulmonary capillary wedge pressure, QRS duration, severity of mitral regurgitation, body mass index, New York Heart Association class and the presence of atrial fibrillation with these events. During follow-up, 23 patients reached the primary endpoint. In a multivariate analysis, EF (chi-square 5.74, p=0.0166), severity of mitral regurgitation (chi-square 12.31, p=0.0004), and QRS duration (chi-square 11.20, p=0.0008) remained significant predictors. Conclusion In NIDCM patients, prolonged QRS duration is a high risk factor for remodeling and unfavorable events. The severity of mitral regurgitation was also a strong risk predictor. (Circ J 2006; 70: 57 - 62)