Left ventricular hypertrophy (LVH) is an independent risk factor for cardiac mortality in adults with end-stage renal disease (ESRD). It is prevalent in pediatric patients on chronic dialysis. The objectives of this study were to evaluate left ventricular mass (LVM) in children and adolescents at the initiation of dialysis and to assess its changes during chronic dialysis therapy. In this longitudinal analysis, 29 patients aged 4–18 years had an echocardiographic evaluation within 90 days of starting dialysis therapy and a follow-up study at least 6 months later. LVH was defined as LVM index (g/m^2.7) >95th percentile for normal children and adolescents. On the initial echocardiogram 20 of 29 (69%) patients had LVH and 24 patients (83%) had abnormal LV geometry (38% eccentric LVH, 31% concentric LVH, and 14% concentric remodelling). Patients with LVH were more likely to be on antihypertensive medications (16/20) than patients without LVH (3/9) (P=0.005). Repeat echocardiogram, performed after 10±3 months on chronic dialysis, showed no significant difference in the mean LVM index (49.6±17.5 g/m^2.7 and 49.7±16.1 g/m^2.7, respectively) or in the prevalence of LVH or LV geometric pattern. However, 14 of 29 patients had a progressive increase in LVM index and 15 patients had regression. Multiple regression analysis showed that baseline LVM index (P=0.005) and interval change in indexed systolic blood pressure (P=0.027) were independent predictors for LVM index changes. In summary, LVH and abnormal LV geometry are already prevalent in children and adolescents with renal failure at the time of initiation of dialysis therapy, indicating that LVH develops during the pre-ESRD course. Early intervention to control blood pressure may be an important factor to improve and prevent progression of LVH in pediatric patients with ESRD.