Objectives: The present study focused on analysing the relationship between body composition and blood pressure in children and adolescents. Methods: The sample consisted of 1025 schoolchildren between 3 and 21 years of age (519 boys and 506 girls). The systolic blood pressure (SBP, mmHg) and diastolic blood pressure (DBP, mmHg) were measured with the Visomat Comfort 20/40 arm tensiometer. The following body composition variables were studied: height (m), weight (kg), body mass index (BMI; kg/m2), fat mass (FM; % and kg), fat-free mass (FFM; % and kg), Fat Mass Index (FMI; kg/m2), Fat Free Mass Index (FFMI; kg/m2), total body water (TBW; % and kg), waist (cm), hip (cm), Waist/Hip Ratio (WHR), basal metabolism (BM, Kcal/day). The body composition was evaluated using the Tanita BC 418-MA body composition analyzer, the height was measured with a HM-250P Leicester stadiometer, and the waist and hip perimeter were measured with a tape measure. The statistical analysis was carried out with the Statistical Package for Social Sciences 23.0. Findings: SBP and DBP were significantly (p<0.05) correlated with all the body composition variables studied, with the exception of the relationship between WHR and DBP. The correlations were positive between blood pressure (SBP and DBP) and the following body composition variables: height, weight, BMI, FM (kg and %), FMI, FFM (Kg), FFMI, TBW (Kg), waist, hip, WHR, and BM. The correlations were negative between blood pressure (SBP and DBP) and the following body composition variables: FFM (%) and TBW (%). Conclusions: The body composition and blood pressure of children and adolescents are closely related, so intervention programs through physical activity to improve body composition would be also an appropriate strategy to reduce the risk of hypertension.