Acinetobacter infections cause treatment failures especially in intensive care units because of multiple antibiotic resistance. The purpose of this study was to investigate the in-vitro effect of antibiotic combinations on 12 multiresistant Acinetobacter strains. The in vitro synergy of sulbactam-ampicillin + ciprofloxacin (SAM+CIP), sulbactam-ampicillin + amikacin (SAM+AK), imipenem + ciprofloxacin (IMP+CIP) and imipenem + amikacin (IMP+AK) combinations were studied by the checkerboard technique in multiresistant strains. The highest rates of synergy were detected with SAM+AK (3/12) combination. Indifference was found to be 91.6%, 75%, 75% and 83.3% in SAM+CIP, SAM+AK, IMP+CIP and IMP+AK combinations, respectively. In conclusion, combination therapy should be applied and in vitro synergy tests should be performed before starting treatment in multiresistant Acinetobacter infections.