The purpose of this study was to determine the prevalence and prognostic role of left ventricular reverse remodeling (LVRR) in idiopathic dilated cardiomyopathy (IDCM).Tailored medical therapy can lead to LVRR in IDCM. The prevalence and prognostic impact of LVRR remain unclear.We consecutively enrolled 361 IDCM patients. LVRR was defined as a left ventricular ejection fraction increase of ≥10 U or a left ventricular ejection fraction of ≥50% and a decrease in indexed left ventricular end-diastolic diameter of ≥10% or indexed left ventricular end-diastolic diameter of ≥33 mm/m(2) at 24 months (range 9 to 36 months). Follow-up echocardiographic data were available for 242 patients (67%), 34 (9%) died/underwent heart transplantation (HTx) before re-evaluation, and 85 (24%) did not have a complete re-evaluation. After re-evaluation, the surviving patients were followed for 110 ± 53 months; there were 55 deaths (23%) and 32 HTx (13%).LVRR was found in 89 of 242 patients (37%). Baseline predictors of LVRR were higher systolic blood pressure (p = 0.047) and the absence of left bundle branch block (p = 0.009). When added to a prognostic baseline model including male sex, heart failure duration, New York Heart Association functional classes III to IV, LVEF, significant mitral regurgitation, and beta-blockers, LVRR, New York Heart Association functional classes III to IV, and significant mitral regurgitation after 24 months emerged as independent predictors of death/HTx and heart failure death/HTx. The model including follow-up variables showed additional prognostic power with respect to baseline model (for death/HTx, area under the curve: 0.80 vs. 0.70, respectively, p = 0.004). Furthermore, only LVRR was significantly associated with sudden death/major ventricular arrhythmia in the long-term.LVRR characterized approximately one-third of IDCM patients surviving 2 years while receiving optimal medical therapy and allowed a more accurate long-term prognostic stratification of the disease.