PURPOSE: Infection is a major complication in patients with malignant disease. This study was performed to identify the causes and the etiologic agents of febrile infections and to characterize the clinical courses including the response to antimicrobial agents inpediatric cancer patients. METHODS: This study reviewed 274 febrile episodes occurring in 163 children with neoplastic disease which were indentified prospectively at Seoul National University Children's Hospital from January, 1991 to June, 1993. Neutropenia was defined as [granulocyte+band from] < or = 500mm(3). Each febrile episode was classified as a microbiologically documented infection(MDI), a clinically documented infection(CDI), and a probale infection(PI). The responses to initial antimicrobial atents were categorized into improvement, temporary improvement, failure, and not evaluable according to period to defervescence. RESULTS: Seventy seven percent of the febrile epidodes developed in neutropenic state. MDI were 98(36%), CDI 92(34%), and PI 84(30%) episodes. Bacteria were isolated in 75%, viruses in 13% and fungi in 11% of MDI. Fifty two episodes(19% of all) were associated with a bacteremia, and focal infections were indentified in 63% of bacteremia. The most frequent organisms causing MDI were E. coli(22%), K. pneumoniae(15%), S.epidermidis(7%). The great majority of infections other than bacteremia ocurred in the lung(32%), oral cavity(17%), skin and soft tissue(13%), and urinary tract(11%). The frequency of antimicrobial resistance of causative organisms was high. The responses to initial antimicrobial agents were improvement in 49%, temporary improvement in 13%, and failure in 38%. Patients with bacteremia responded less well than those with other categories. Mortality was 7% of total episodes. All of the fatal cases occurred in neutropenia and all but one had hematologic malignancies. CONCLUSIONS: This study documents the etiology and the type of infections and the responses to antimicrobial therapy in children with neoplastic diseases. The changes of causative agents and antimicrobial resistance should be considered in therapeutic strategies of cancer infection.