Objective: The aim of this study was to investigate the distribution and antibiotic susceptibility of Acinetobacter species isolated in our hospital in the last six years. Method: Acinetobacter species isolated from various clinical samples sent to Ondokuz Mayis University, Medical Faculty Hospital Central Laboratory, Bacteriology Sub - Discipline Laboratory between January 2006 and June 2011 were included. Conventional methods and Vitek 2 Compact (bioMérieux-SE, France) automated systems were used for the identification and antibiotic susceptibility of the isolates. Results: During the study period, a total of 3212 Acinetobacter species were isolated. Species distribution of Acinetobacter isolates and their ratios were found as follows: Acinetobacter baumannii - Acinetobacter calcoaceticus complex (n=3006; 93.6%), Acinetobacter lwoffii (n=83; 2.6%), Acinetobacter junii (n=27; 0.8%), Acinetobacter haemolyticus (n=19; 0.6%) and Acinetobacter spp. (n=77; 2.4%). Acinetobacter isolates were isolated at the most from tracheal aspirate samples (n=747; 23.2%) and samples sent from intensive care units (n=705; 21.9%). Ceftazidime resistance increased from 70.2% to 82.7%; cefepime from 26.4% to 79.7%; imipenem from 27.2% to 77.2%; meropenem from 4.5% to 77% and ciprofloxacin from 40.4% to 78.9% in the last six years. In the first six months of 2011, the resistance ratios to tigecycline and colistin were determined as 5.9% and 0.2% respectively. No significant changes were observed in ampicillin-sulbactam resistance ratios. Conclusion: As of the first half of 2011, when all the findings were evaluated, high-rate of resistance to cefepime, piperacillin-tazobactam, ceftazidime, ceftriaxone, meropenem, imipenem, ciprofloxacin and levofloxacin were determined and it was observed that this level had a tendency to increase. Colistin resistance in Acinetobacter species was observed as minimal. The reduction seen during the years in the resistance rate of gentamycin, an antibiotic from the aminoglycoside group, was attributed to its less frequent use in recent years. As shown in our study, generally antibiotic resistance is gradually increasing in Acinetobacter species. In the future, new antibiotics will be required for the treatment of infections caused by Acinetobacter species. In conclusion, we are in the opinion that rate of appearance of pan-resistant strains which may pose serious problems in the near future should be decelerated by promoting the rational use of antibiotics.