Despite the importance of hypertension in adults, its effects on child health are poorly understood. This cross-sectional epidemiological study was designed to look for a relationship between elevated blood pressure (BP) in children and 24-h urinary excretion of sodium (Na) and potassium (K), and between BP and dietary salt intake. The study population was all 59 856 schoolchildren aged 6 to 14 years in the province of Almería in southern Spain, among whom 613 participants were chosen randomly for study. We measured 24-h urinary Na and K concentrations, systolic and diastolic BP, body weight and height. There was a weak correlation between Na excretion and systolic BP (r = 0.18, 95% confidence interval 0.10-0.26), and between K excretion and systolic BP (r = 0.49, 95% CI = 0.04 -0.20). Body