Urinary tract infections (UTI) are considered the most common, non-epidemic bacterial infectious disease. During infancy and childhood, about 5% of girls and 0.5% of boys will be affected by at least one episode of UTI . During the neonatal period more males than females are affected. Thereafter, the incidence of UTI in males declines rapidly  whereas girls remain prone to infections at about the same rate until the onset of puberty [5, 10, 31]. Although no serious consequences will arise in the majority of UTI patients, some risks have to be pointed out: 50% of the patients will suffer from recurrent UTI [11, 31]; the formation of renal concrements is increased in UTI-prone individuals, eventually leading to further complications; renal scars develop in about 10% of the patients even without urinary tract obstruction [11, 31, 39, 40, 58]; 20% of patients with segmental renal scars will develop arterial hypertension [4, 31]; a few UTI patients are at risk of ending up with chronic renal failure . Anatomical and urodynamical abnormalities, immunological and bacteriological factors predispose to UTI and influence the course of the disease [10, 44]. Obstructive uropathy, renal malformations, vesico-uretero-renal reflux and neurogenic bladder dysfunction with formation of residual urinary volume facilitate bacterial colonization and subsequent infection of the urinary tract (Table 1). Children with obstructive anomalies will be cured by surgical correction of the underlying disorder; elimination of the residual urinary volume in patients with neurogenic bladder dysfunction (for instance by intermittent catheterization) will have the same positive effect: in those cases the causal effect of the underlying pathology is obvious.