Escherichia coli is the most commonly isolated organism from pediatric patients with UTIs. However, any organism that gains access to the urinary tract system may cause infection, including fungi (Candida species) and viruses. Pyelonephritis may lead to renal scarring and long-term complications, such as hypertension and chronic renal failure. (Approximately 10-30% of children with UTI develop renal scarring).Among the patients who are attending the general and nephrology outpatient clinic in Abu El Reesh hospital Cairo University, forty ( 40) cases with documented UTI were included in this study during the period from March 2010 to December 2010, to evaluate the effect of oral antibiotics versus the intravenous antibiotics in the treatment of UTI in children .