Seventy-seven cases of bacteremia due to Achromobacter xylosoxidans were reviewed, and susceptibility studies were performed on 11 clinical isolates of A. xylosoxidans. Nosocomial bacteremia was noted in 54 of 77 patients (70%), and 28 (36%) had infection associated with an outbreak or acquired from a discrete point source. The most common underlying illnesses were malignancies (30%) and cardiac disease (21%); immunosuppression affected 27%. The most common clinical syndromes were primary and catheter-associated bacteremia (19% each) and pneumonia (16%). The case-fatality rate was 30%; only 3% of patients with primary or catheter-associated bacteremia died, but 65% of patients with meningitis, endocarditis, and pneumonia died. The case-fatality rate in neonates was 80%. Susceptibility studies showed that all strains were resistant to aminoglycosides, most were resistant to quinolones, and all were susceptible to broad-spectrum penicillins, imipenem, ceftazidime, and trimethoprim-sulfamethoxazole. Two-disk approximation and time-kill studies showed synergy or additive effects for the combination of gentamicin and piperacillin against most strains.