A 1-year prospective study of patients with a positive blood culture and admitted through the emergency department (ED), was conducted to detect incidence and risk factors for resistance of Enterobacteriaceae to gentamicin and ciprofloxacin. A total of 245 emergency department-admitted patients had positive blood cultures, of which 131 (54%) grew Enterobacteriaceae. Of these 131 isolates, 32 (24%) were resistant to gentamicin and 37 (28%) to ciprofloxacin. Risk factors, by multivariate analysis, for gentamicin and ciprofloxacin resistance were: male gender (P<0.05 and P<0.01, respectively), nursing home residence (P<0.001), diabetes mellitus (P<0.05) and presence of a foreign body (P<0.05 and P<0.005). An additional risk factor for ciprofloxacin resistance was recent hospitalisation (P<0.05). These data facilitate optimal selection of empirical antibiotic treatment of suspected Gram-negative infections, and may contribute to improved patient outcome and optimal use of antibiotics.