Acinetobacter spp. have a special role in nosocomial infections. They usually colonize intensive care units and cause infections. Multiple antibiotic resistance is observed to be an important problem in Acinetobacter isolates in recent years. The aim of this study was to evaluate the susceptibilities of 277 Acinetobacter baumannii strains (99 blood, 71 abscess, 26 urine, 81 lower respiratory tract isolates) isolated from adult patients hospitalized in Ankara University Ibni Sina Hospital during one year period in 2002. The resistance rates of the strains against studied antibiotics were found as follows; 31.2% for netilmicin, 44.6% for sulbactam-cefoperazone, 53.6% for imipenem, 59.8% for amikacin, 59.9% for tobramycin, 74% for ciprofloxacin, 78% for gentamicin, 78.3% for ticarcillinclavulanate. 79.5% sulbactam-ampicillin, 82.3% for cotrimoxazole, 84.8% for ticarcillin, 87.3% for piperacillin-tazobactam, 88.1% for ceftazidime and 92.1% for piperacillin. When the isolates obtained from the reanimation unit were compared with the isolates obtained from the other hospital units, a significantly high level of resistance was found from the isolates obtained from the reanimation unit except netilmicin and sulbactam/cefoperazone. The high rate of in-vitro antibiotic resistance of the A. baumannii strains indicated the importance of controlled antibiotic usage and appliance of hospital infection control measures.