Prognostic significance between progression of left ventricular hypertrophy (LVH) and clinical outcomes in patients with ST-elevation myocardial infarction (STEMI) is uncertain. The objective of this study was to investigate prognostic impact of progression of LV mass index (LVMI) in patients with STEMI.We analyzed the data and clinical outcomes of patients with STEMI who received successful coronary intervention. A total of 200 patients who had echocardiographic follow-up between 12 and 36 months were finally enrolled. According to change in LVMI compared to baseline LVMI, patients were classified into progression group and nonprogression group. Progression of LVMI was defined when increment of LMVI was greater than 10% compared to baseline LVMI. End points were major adverse cardiac events within 5 years, including death, recurrent MI, target vessel revascularization, and hospitalization due to heart failure.Progression of LVMI occurred in 55 patients. In the progression group, rate of recurrent MI was higher (13 vs 2%, P = .026) and the event-free survival of recurrent MI was significantly worse (log-rank P < .001) than that in the nonprogression group. Adjusted hazard ratio of progression of LVMI for recurrent MI was 10.253 (95% confidence intervals 2.019-52.061, P = .005).Increased LVMI was an independent predictor for adverse events, especially for recurrent MI, in patients with STEMI.