BACKGROUND: The purpose of this study was to evaluate the etiologic organisms, risk factors, and other infectious features of febrile neutropenic patients developing septic shock. METHODS: We reviewed medical record of 457 patients developing neutropenic fever after chemotherapy or hematopoietic stem cell transplantation (HSCT) at Catholic HSCT Center from Jan 1998 to Dec 1999. Out of them, age/sex matched patients without septic shock were enrolled into the control group, and retrospective case-control study was conducted. RESULTS: Overall incidence of septic shock was 8.5%. Most common underlying disease of the two groups was acute leukemia. Microbiologically defined infection (MDI), especially Gram-negative bacterial infection, was significantly more common in the septic shock group than in the control group. Escherichia coli was the most common organism in the two groups (51.3% vs 27.7%, P<0.001). However, empirical use of glycopeptide was more frequent in the shock group (P<0.05). Differing from other report, fatal infection due to viridans streptococci was not observed in spite of quinolone prophylaxis. Mean leukocyte count at the onset of fever was 207/mm3 and 355/mm3 (P=0.027) and mean duration of total febrile day was 12.3 days and 7.8 days, respectively (P=0.001). On multivariate analysis, MDI and leukocyte count at the onset of fever were the significant risk factors for the septic shock. Overall mortality showed higher tendency in the shock group than in the control group (23.1% vs. 12.0%, P=0.057). Especially, in patients with Gram-positive bacterial infection, infection related mortality was significantly higher in the shock group than in the control group (50% vs. 8.9%, P=0.013). CONCLUSION: Although Gram-positive bacterial infection has been increasing, Gram-negative bacteria, including E. coli, were the most common causative organisms for sepctic shock in febrile neutropenic patients. However, considering high mortality in the septic shock caused by Gram-positive bacteria, glycopeptide must immediately be administered to the febrile neutropenic patients developing septic shock.