BACKGROUND: Newer approaches for classifying gradations of pediatric obesity by level of body mass index (BMI) percentage above the 95th percentile have recently been recommended in the management and tracking of obese children. Examining the prevalence and persistence of severe obesity using such methods along with the associations with other cardiovascular risk factors such as hypertension is important for characterizing the clinical significance of severe obesity classification methods. METHODS: This retrospective study was conducted in an integrated healthcare delivery system to characterize obesity and obesity severity in children and adolescents by level of body mass index (BMI) percentage above the 95th BMI percentile, to examine tracking of obesity status over 2-3 years, and to examine associations with blood pressure. Moderate obesity was defined by BMI 100-119 % of the 95th percentile and severe obesity by BMI >=120 % x 95th percentile. Hypertension was defined by 3 consecutive blood pressures >=95th percentile (for age, sex and height) on separate days and was examined in association with obesity severity. RESULTS: Among 117,618 children aged 6-17 years with measured blood pressure and BMI at a well-child visit during 2007-2010, the prevalence of obesity was 17.9 % overall and was highest among Hispanics (28.9 %) and blacks (20.5 %) for boys, and blacks (23.2 %) and Hispanics (21.5 %) for girls. Severe obesity prevalence was 5.6 % overall and was highest in 12-17 year old Hispanic boys (10.6 %) and black girls (9.5 %). Subsequent BMI obtained 2-3 years later also demonstrated strong tracking of severe obesity. Stratification of BMI by percentage above the 95th BMI percentile was associated with a graded increase in the risk of hypertension, with severe obesity contributing to a 2.8-fold greater odds of hypertension compared to moderate obesity. CONCLUSION: Severe obesity was found in 5.6 % of this community-based pediatric population, varied by gender and race/ethnicity (highest among Hispanics and blacks) and showed strong evidence for persistence over several years. Increasing gradation of obesity was associated with higher risk for hypertension, with a nearly three-fold increased risk when comparing severe to moderate obesity, underscoring the heightened health risk associated with severe obesity in children and adolescents.