Based on outcome data, surgery is recommended for asymptomatic adults with chronic mitral regurgitation (MR) and systolic dysfunction, marked left ventricular (LV) dilation, pulmonary hypertension, atrial fibrillation, or high likelihood of successful repair; but indications for children are poorly defined. We sought to determine predictors of postoperative LV dysfunction in asymptomatic children with chronic MR. The surgical database was searched for all children who underwent mitral valve surgery for chronic MR (2000-2012). Exclusion criteria were preoperative symptoms, acute MR, cardiomyopathy, or other defects affecting LV size. Preoperative and latest follow-up clinical and echocardiographic data were obtained. LV dysfunction was defined as ejection fraction (EF) ≤55% or shortening fraction (SF) ≤28%. Associations between preoperative factors and late LV dysfunction were determined using univariate Poisson regression. For the 25 children who met criteria, preoperative median LV end systolic Z score (LVESZ) was 5.3, EF was 65%, and SF was 34%. At follow-up (median 3.9 years), nine patients (36%) had LV dysfunction. Lower preoperative SF (OR 0.6, p < 0.001) and higher LVESZ (OR 1.7, p < 0.01) were associated with late LV dysfunction. LVESZ ≥ 5 combined with SF ≤ 33% had a sensitivity of 89%, specificity of 88%, and negative predictive value of 93% for late LV dysfunction. Only 1/14 patients with preoperative SF > 33% had late LV dysfunction. For asymptomatic children with chronic MR, surgery should be considered before LVESZ exceeds five and SF falls below 33%. Patients with SF > 33% may be followed with serial echocardiographic measurements.