We determined the sensitivity of waist-to-height ratio (WHtR) as a marker for high blood pressure in children aged nine to 15 years (n = 1 131), from schools in the North West province, South Africa. Anthropometric and blood pressure measurements were taken. The sensitivity and specificity of the WHtR to identify children with high blood pressure were evaluated. At a cut-off value of 0.5, 7.9% of the girls and 3.4% of the boys had central adiposity. Thirteen per cent of the children were hypertensive. The optimal WHtR cut-off value to identify children with hypertension was 0.41 in both boys and girls. Positive correlations were observed between anthropometric indices. Using linear regression analyses, age and body mass index were significant predictors of high blood pressure in boys, while for girls it was height and weight. Results suggest that adopting a WHtR cut-off value < 0.5 could enhance the use of WHtR as a marker for high blood pressure in children.