Intensive Care Unit, General Hospital of Lamia, 2Microbiology Laboratory, General Hospital of Lamia Nosocomial infections caused by Acinetobacter baumannii are of increasing concern in critically ill patients and the emergence of multi-drug resistant strains (MDRAB) complicates their treatment. The purpose of this retrospective study was to determine the incidence of MDRAB infections, as well as PNEUMON Number 3, Vol. 19, July - September 2006 229 to investigate the effect of antibiotic treatment on mortality. Medical records of all ICU admissions through a 21-month period were reviewed (N 240); patients with MDRAB-positive cultures were eligible for evaluation (N 35). According to infection type and origin, eligible patients were divided into three groups: group A included patients with ventilator-associated pneumonia (VAP); group B patients with sepsis of non-respiratory origin; and group C patients with respiratory colonization. The overall incidence of MDRAB-positive cultures was 14.58%. Of them, 71.4% of the patients (N 25) had VAP; 14.2% had sepsis of non-respiratory origin (N 5); and 14.2% (N 5) had respiratory colonization. Mean age was 58.14 years; male-to-female ratio was 21/14; and mean APACHE II score at ICU admission 18.2. The most important risk factors were CHF, CAD, COPD and surgical procedure. Treatment included ampicillin/sulbactam and colimycin alone or in combination. Crude mortality was 25.71% (N 9) and disease-specific mortality 23.33% (N 7). Clinical improvement was noted in 70% (N 21) and chronic colonization developed (group C encountered) in 11.42% (N 4). The incidence of infections due to MDRAB among ICU patients is clinically significant. VAP is the most frequently encountered infection. Combination treatment with ambicillin/sulbactam plus colimycin seems to be more effective due to the synergistic effects of colimycin and sulbactam, as evidenced by a reduction in mortality, which was nevertheless not statistically significant. Our results are based on a small series of patients and larger well-designed studies are needed to determine the efficacy of colimycin in combination treatment. Pneumon 2006, 19(3):231-237.