OBJECTIVES: To evaluate the clinical and economic impact of bacteremia caused by extended-spectrum beta-lactamases (ESBL) producing Escherichia coli. METHODS: A case-control study was conducted in a teaching hospital in Hong Kong. Case patients who had blood cultures positive for ESBL-producing E. coli were matched with patients who had bacteremia caused by non-ESBL-producing E. coli from January 2002 through December 2004. Demographic data, clinical factors and health care resource utilization for bacteremia were retrieved from medical records. Outcome measurements included mortality, infection-related cost and infection-related length of stay. RESULTS: Thirty-five case patients with ESBL-producing E. coli bacteremia were matched with 35 control patients with non-ESBL-producing E. coli bacteremia. The mortality rates were 8/35 (22.9%) in cases and 1/35 (2.9%) in controls. The average total cost for cases and controls were HK$51,100 ± $44,292 and HK$30,300 ± $19,427 (USD1=HKD7.8), respectively. Mean infection-related length of stay in cases was 11.5 ± 4.9 days and 8.4 ± 5.2 days in controls. Multiple regression analysis showed that ESBL production was not significantly associated with mortality, but it was a significant predictor of infection-related cost (ME: 1.32; 95% CI=1.04-1.69; P <0.001) and infection-related length of stay (ME:1.42, 95% CI=1.16-1.73, P = 0.001). CONCLUSIONS: ESBL-production was associated with increased length of stay and direct medical cost for treatment of E. coli bacteremia.