Fifty-four children were diagnosed as pyelonephritis caused by extended-spectrum β-lactamase-producing Enterobacteriaceae at the largest children's hospital in Japan. Although 32 (59%) patients were treated with antimicrobials that are ineffective against the organisms, 39 (72%) patients became afebrile ≤2 days and clinical outcome was excellent. Children with pyelonephritis caused by extended-spectrum β-lactamase-producing Enterobacteriaceae can be successfully treated with noncarbapenem antimicrobials.