BACKGROUND: Ambulatory hypertension is associated with elevated left ventricular mass index (LVMI), cardiac dysfunction, and increased arterial stiffness in adolescents. Whether the addition of measures of BP variability improves the prediction of subclinical cardiovascular target organ damage (TOD) over mean BP measures is not known. METHODS: We assessed clinic and ambulatory BP (ABP), anthropometrics, and TOD in 397 adolescents. ABP means standard deviation (SD), BP, and heart rate (HR) dipping were calculated; coefficients of variability (CV) were calculated (SD/mean) to assess ABP variabilities. Measures of TOD included LVMI, left ventricular hypertrophy (LVH), LV systolic shortening, LV diastolic function (e'/a'), and pulse wave velocity. General linear models were used to determine if increased ABP variability measures were significant determinants of TOD in models containing mean ABP percentiles, age, sex, race/ethnicity, BMI z-score, and HR. RESULTS: Mean participant age was 15.6 ± 1.7 years (63% white, 59% male) with mean casual BP 122.6/71.6 mmHg ±12.4/10.5, and mean awake systolic ABP 124.2/72.0 ± 11.3/7.7 mmHg. In linear models, increased awake CV-DBP and HR dipping were significant determinants of LVMI. CV-HR was an independent determinant of diastolic (e'/a') but not systolic dysfunction. Using logistic regression, the combination of awake and asleep diastolic ABP variability and awake systolic ABP percentile improved the prediction of LVH. CONCLUSIONS: Consideration of ABP variability in addition to ABP percentile may aid in identifying adolescents at risk for LVH.