Hypertension in children is defined as sustained elevated blood pressure (BP) over several visits. For the screening of hypertension, it is standard to obtain several BP readings at the initial visit. There is however no recommendation on the minimum number of readings needed. We evaluated the performance of BP readings obtained at one initial screening visit to predict the diagnosis of hypertension in children. In a school-based study conducted in Switzerland, BP was measured three times on up to three visits in 5207 children. Sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) of elevated BP at the initial screening visit for the identification of hypertension were estimated using the 1st, 2nd, and 3rd BP readings (R1, R2, R3), as well as (R1 + R2)/2 and (R1 + R2 + R3)/3). These performance indices were compared with the reference method (R2 + R3)/2. The ability of BP readings to discriminate children with and without hypertension was evaluated with receiver operating characteristic curve analysis. The prevalence of systolic/diastolic hypertension was 2.2%. The greatest performance to identify children with hypertension was obtained with R2 (sensitivity: 97%; specificity: 88%; PPV: 15%; NPV: 100%) and the reference method, (R2 + R3)/2 (sensitivity: 100%; specificity: 90%; PPV: 18%; NPV: 100%). The ability to discriminate using R1, R2, (R1 + R2)/2, and (R2 + R3)/2 for the identification of hypertension was strong (AUC: 0.89, 0.93, 0.92, and 0.95, respectively). Obtaining two BP readings and using only the second one at a screening visit may be sufficient as initial step for the identification of hypertension in children.