To compare pediatric ambulatory blood pressure monitoring (ABPM) criteria with adult ABPM criteria for the diagnosis of hypertension and detection of left ventricular hypertrophy (LVH) in adolescents. ABPM and echocardiography reports from adolescents age 13-21 years from 2015 to 2019 were analyzed. The concordance of hypertension based on pediatric criteria (American Heart Association 2014) was compared with adult criteria from American College of Cardiology/American Heart Association 2017 (overall BP ≥125/75 mm Hg, wake BP ≥130/80 mm Hg, sleep BP ≥110/65 mm Hg) using the Cohen kappa statistic. Logistic regression, adjusted for body mass index z score, and receiver operating characteristic curves (ROCs) compared pediatric criteria vs adult criteria in predicting LVH (left ventricular mass index >95th percentile reference values and left ventricular mass index >51 g/m2.7). Of 306 adolescents, 140 (45.8%) had hypertension based on pediatric criteria vs 228 (74.5%) based on adult criteria; the agreement was poor (59.3%, n = 137, kappa = 0.41). A higher prevalence of LVH was captured by adult criteria only (n = 91) compared with pediatric criteria only (n = 3). Logistic regression found no significant differences between pediatric and adult criteria in the detection of LVH >95th percentile (OR 1.24, CI 0.66, 2.31, P = .51) or >51 g/m2.7 (OR 1.06, CI 0.47, 2.40, P = .89). ROCs for pediatric criteria were not significant for detecting LVH >95th percentile (0.50, P = .91) or >51 g/m2.7 (0.55, P = .45), whereas the ROC for adult criteria was significant for detecting LVH >95th percentile (0.59, P = .045) but not >51 g/m2.7 (0.63, P = .07). Although all individuals with LVH >51 g/m2.7 were hypertensive by adult criteria, 8 of these individuals were missed by pediatric criteria. Adult criteria captured a higher prevalence of LVH and appeared to predict better LVH than pediatric criteria. A consideration to align ABPM criteria for diagnosing hypertension in adolescents with adult guidelines is warranted.