Acute urinary tract infection (UTI) is among the most common bacterial infections in infants and children. Diagnosis requires evidence of infection and the presence of at least 50,000 colony-forming units (CFU)/mL of a pathogen cultured from an appropriately collected urine specimen. Febrile UTIs (ie, temperature 38°C [100.4°F] or greater) are most common during the first two years of life. Risk factors for UTI in febrile female infants are white race, age younger than 12 months, temperature 39°C (102.2°F) or greater, fever lasting 2 days or more, and absence of another source of infection. For febrile male infants, risk factors include being uncircumcised. If circumcised, risk factors include nonblack race, temperature 39°C (102.2°F) or greater, fever for more than 24 hours, and absence of another source of infection. Antibiotic treatment should be continued for 7 to 14 days. Renal and bladder ultrasonography is indicated for infants ages 2 to 24 months with a febrile UTI. If ultrasonography results are abnormal, a voiding cystourethrogram (VCUG) is indicated. VCUG also is indicated for children with recurrence of febrile UTI to identify vesicoureteral reflux and/or other anatomic findings associated with recurrent UTI. Recent studies have shown a statistically significant benefit of continuous antibiotic prophylaxis for prevention of recurrent UTI.