Urinary tract infection (UTI) is one of the commonest conditions of childhood, affecting an estimated 10% of girls and 3% of boys in the first 16 years of life. Whereas asymptomatic bacteriuria and low-grade lower tract infection pose little or no risk of renal damage, pyelonephritis can cause severe systemic illness and poses a significant threat of long-term renal morbidity. The principal aim of investigation is to identify underlying abnormalities of the urinary tract, notably vesicoureteric reflux. Guidelines on investigation and management published by the National Institute of Clinical Excellence will be reviewed in this chapter. Treatment of dysfunctional voiding and other features of ‘elimination syndrome’ plays an important role in the prevention of urinary tract infection in this age group.