OBJECTIVE: Infections due to P. aeruginosa are associated with increased likelihood of death and morbidity. Empiric therapy is often difficult due to increased resistance noted with this organism. The purpose of this study was to determine the impact of inappropriate initial empiric therapy on health outcomes of patients with P. aeruginosa bacteremia. METHODS: Retrospective cohort study of hospitalized patients with their first episode of P. aeruginosa bacteremia. Patients were stratified based on appropriateness of antipseudomonal therapy. Inappropriate initial empiric therapy was defined as receipt of antibiotic therapy to which the isolate displayed in vitro resistance. Data collected included discharge mortality, new ICU admit, new requirement for ventilator therapy or hemodialysis, and length of hospital stay. RESULTS: A total of 87 patients (71% males/29% females) aged 58±17 years (mean±SD) were identified between January, 2002 to April, 2004. Overall mortality was 44%. Forty-nine percent of patients' received inappropriate antibiotic therapy. ApacheII score were significantly higher in patients that died (p=0.003). Mortality rates were significantly higher in patients treated with inappropriate empiric therapy (63%) compared to patients treated appropriately (39%, OR=2.97, p=0.024). New requirements for ICU admission, hemodialysis, or ventilator did not differ between the two groups. CONCLUSIONS: Inappropriate initial empiric therapy in patients with P. aeruginosa bacteremia significantly increased mortality rates.