Severe infection is a major cause of morbidity and mortality in patients with malignancy. In this study, 34 episodes of septicemia occurred in 1,468 childhood patients with malignancy who admitted and were treated at National Sapporo Hospital between 1979 and 1988. The occurrence of septicemia and its mortality rate were higher in malignant hematologic disease than in malignant solid tumor. Most cases of septicemia occurred in relapse. The most frequent organism causing septicemia were Klebsiella pneumoniae (16.3%) and Staphylococcus epidermidis (16.3%). Septicemia due to Gram-negative organism was more frequent than that of Gram-positive organism or fungus. Polymicrobic septicemia occurred 3 times and multiple episodes 6 times. They had a high mortality rate. Neutropenia was strongly associated with episode of septicemia. In our series, absolute neutrophil count under 500 per microliter developed septicemia. Especially, children with less than 100 granulocytes per microliter had a major risk factor for the development of infection and death. No children with granulocyte count greater than 1000 per microliter died in connection with septicemia.