The American Academy of Pediatrics (AAP) recommends that any child diagnosed with hypertension have an echocardiogram to evaluate for the presence of left-ventricular (LV) hypertrophy (LVH) and advocates that LVH is an indication to initiate or intensify antihypertensive therapy. However, there is no consensus on the ideal method of defining LVH in the pediatric population. Many pediatric cardiologists rely on wall-thickness z-score of the LV posterior wall and/or interventricular septum to determine LVH. Yet, the AAP advocates using LV mass indexed to 2.7 (LVMI(2.7)) ≥ 51 g/m(2.7) to diagnose LVH. Recently, age-specific reference values for LVMI ≥ 95% were developed. The objective of the study was to determine the concordance between diagnosis of LVH by wall-thickness z-score and diagnosis by LVMI(2.7) criteria. A retrospective chart review was performed for subjects diagnosed with hypertension at a single tertiary care center (2009-2012). Echocardiogram reports were reviewed, and assessment of LVH was recorded. Diagnosis of LVH was assigned to each report reviewed according to three criteria: (1) LV wall-thickness z-score > 2.00; (2) age-specific reference values for LVMI(2.7) > 95th percentile; and (3) LVMI(2.7) > 51 g/m(2.7). Cohen's kappa statistic was used as a measurement of agreement between diagnosis by wall-thickness z-score and diagnosis using LVMI(2.7). A total of 159 echocardiograms in 109 subjects were reviewed. Subjects included 31 females and 77 males, age 13.2 ± 4.4 years, and 39 (42%) with a diagnosis of secondary hypertension. LVH was diagnosed in 31 cases (20%) based on increased wall-thickness z-score. Using LVMI(2.7) > 95%, LVH was found in 75 (47%) cases (mean LVMI(2.7)42.3 ± 17.2 g/m(2.7) [range 11.0-111 g/m(2.7)]). The wall-thickness z-score method agreed with LVMI(2.7) > 95% diagnosis 71% of the time (kappa 0.4). Using LVH criteria of LVMI(2.7) ≥ 51 g/m(2.7), 33 (21%) subjects were diagnosed with LVH. There was 79% agreement in the diagnosis of LVH between the wall-thickness z-score method and LVMI(2.7) > 51 g/m(2.7) (kappa 0.37). There is poor concordance between the diagnosis of LVH on echocardiogram reports using wall-thickness z-score and diagnosis of LVH using LVMI(2.7) criteria. It is important to establish a consensus method for diagnosing LVH because of the high frequency of cardiovascular complications in children with hypertension.