The aim of this study was to determine the prevalence of hypertension in overweight or obese pediatric subjects using different national or international references, which are based either on the entire population or on normal weight children only: 188 centers from Germany, Austria, and Switzerland participated in the Adipositas Patienten Verlaufsbeobachtung initiative. Data from 57,915 children aged 6 to 18 years who are overweight or obese were used to determine the prevalence of prehypertension and hypertension based on Second Task Force, European pooled data, Fourth Report all and Fourth Report nonoverweight, or German Health Interview and Examination Survey for Children and Adolescents (KiGGS) references. Three references included overweight children, whereas 2 (Fourth Report nonoverweight and KiGGS) were based on nonoverweight children only. Based on KiGGS, Fourth Report nonoverweight, Fourth Report all, European pooled data, or Second Task Force, the prevalence of hypertension was 47%, 42%, 36%, 32%, and 27%, respectively. Recent references classified more children as hypertensive, whereas fewer children fell into the prehypertensive group. Only 22% of children were classified as hypertensive by each of the 5 references (8% as prehypertensive). The prevalence of normal blood pressure was independent of the reference applied. Hypertension as defined by the different reference systems was significantly correlated, and all methods were significantly associated with impaired glucose metabolism or dyslipidemia, without significant differences in methods. In conclusion, the diagnosis of elevated blood pressure depends on the reference population used. A nonoverweight reference population substantially increases the prevalence of hypertension in children and adolescents who are overweight or obese. The choice of the reference has significant implications for risk stratification and treatment decisions.