Because host inflammatory response is the final and most important step in the formation of renal scars, the use of anti-inflammatory agents may be the best strategy to reduce renal scarring. In animal studies, the use of corticosteroids has been shown to be effective in preventing post-pyelonephritic scarring. We will conduct a randomized, double-blind, placebo-controlled trial to determine the efficacy of 3 days of daily adjuvant dexamethasone on the incidence of renal scarring 4 to 6 months after a first febrile urinary tract infection (UTI). We hypothesize that the proportion of children with UTI who develop renal scarring will be lower among children who are treated with both dexamethasone and antibiotics as compared with children treated with antibiotics alone.