Renal and perinephric abscesses are a rare but potentially fatal complication of urinary tract infection (UTI). Diagnosing renal and perinephric abscesses has been known to be difficult. These abscesses may occur when the appropriate antibiotic treatment for a UTI is delayed, or in cases with a congenital malformation of the urinary system, especially in children. In the present report, we describe 2 cases of renal abscesses with extra-capsular invasion in children with febrile UTI. A 4-month-old male infant with vesicoureteral reflux developed a renal abscess that infiltrated the perinephric area and the left psoas muscle, despite early antibiotic treatment. A 9-year-old boy with prolonged fever also showed a multi-loculated renal abscess that infiltrated the spleen and diaphragm. Both patients were successfully treated with appropriate antibiotics and percutaneous drainage.