BACKGROUND: Infection is one of the most important and fatal complications in patients with acute leukemia. The characteristics of infection in acute leukemic patients are different from those in other diseases by the lack of normal inflammatory responses or distinct clinical evidence except fever. To improve the outcome of acute leukemia, it is very important to recognize the risk factors, patterns and prognostic factors of acute leukemia. METHODS: We analyzed retrospectively the patterns of infection from 113 febrile patients with acute leukemia from January, 1988 to December, 1995. To determine the prognostic factors and the outcome of infection, the following variables were analyzed: the presence of neutropenia, use of chemotherapeutic agents, type and site of infections, isolated organisms, gastrointestinal decontamination, duration of neutropenia, and bone marrow recovery. RESULTS: Out of 113 febrile patients with acute leukemia, 84 infection episodes(74%) occurred after chemotherapy. The mean duration of neutropenia was 18+/-13 days. The incidence of microbiologically-documented infection(MDI) was 35%(40/113). Pneumonia was the most common infection(26%), followed by primary sepsis(24%), catheter-related infection(9%). In cases of MDI, 63% were caused by gram-negative bacteria, followed by gram-positive bacteria(28%), and fungi(10%). Escherichia coli(25%) was the most common isolated in MDI. Regarding the prognostic factors in cases with infections, the recovery of bone marrow function was the only statistically significant factor(P=0.01). CONCLUSION: Infection has been a major cause of morbidity and mortality in acute leukemic patients. To prevent infection and thereby improve the prognosis of acute leukemia, restoration of bone marrow function at early stage is important.