1. 1. Perinephric abscess is not as rare a disease in infants and children as has been believed. A series of twenty-six proved and six possible cases is presented. 2. 2. To classify patients on the etiologic basis of their lesion as metastatic, complicated by underlying renal disease, or secondary to trauma to the kidney, is important for prognostic and therapeutic reasons. 3. 3. In children, a history which includes urinary complaints or a finding of albumin or white cells in the urine strongly suggests a complicated type of lesion, and indicates a thorough study of the urinary tract. 4. 4. An intravenous pyelogram should be done preoperatively on all patients suspected of having perinephric abscess, unless they are too ill to tolerate the procedure. 5. 5. For metastatic, or traumatic abscess, early incision and drainage is the treatment of choice. 6. 6. In abscess complicating urinary disease, therapy must be individualized and is two-fold in purpose: first, the immediate treatment of the abscess, and second, the subsequent treatment of the underlying urinary tract disease. 7. 7. In metastatic or traumatic abscess in children, the mortality was nil and the hospitalization averaged about three weeks. 8. 8. In abscess complicating urinary disease in children, the mortality was 45 per cent and the hospital stay averaged about ten weeks.