Objective To identify and to determine the antimicrobial susceptibility of Acinetobacter baumannii (A. baumannii) clinical isolates from ICU at Aseer Central Hospital. Methods The study was conducted in the Intensive Care Unit, Aseer Central Hospital, Saudi Arabia over 13 months period (2014-2015). Acinetobacter species (n = 105) were isolated from various clinical samples. Isolates were identified using selected phenotypic criteria and confirmed using the Vitek 2 automated system. This system was used to determine the susceptibilities of 21 antimicrobial agents. Patients, isolates and drug data were analyzed using the SPSS statistical software package to determine some epidemiological and microbiological patterns. Results Of the 105 stains, A. baumannii accounted for 49 (46.67%), A. baumannii complex, 19 (18.09%), A. baumannii/haemolyticus 32 (30.47), Acinetobacter haemolyticus 4 (3.81%), Acinetobater lwoffii 1 (0.95%) and unidentified Acinetobater species 2 (1.3%). Of the 105 Acinetobacter strains, 103 (98.1%) were found multidrug resistant (MDR). A. baumannii strain were 100% sensitive to colistin and 74.5% to trimethoprim + sulfamethoxazole. The remaining 19 antimicrobial agents revealed low or no sensitivities: amikacin 16.3%; ampicillin 7.7%; ceftazidime, 7.3%. Distribution of similar sensitivities was shown by other Acinetobacter species. Mean number of isolates from males and females indicates no statistical variation (P = 0.867) whereas age groups showed significant differences (P = 0.008) as it is clear from the high percentage of infected individuals more than 60 years followed by those aged 20-29 years old (19.05%). Upper respiratory tract (30.48%), lower respiratory tract (47.65%) and subcutaneous tissue (9.5%) were the main sources of Acinetobacter spp. but mean numbers of isolates from these specimens indicate no discrepancy between specimens (P = 0.731). Conclusions Acinetobacter species including A. baumannii were found MDR (98.1%) according to the current Acinetobacter spp. antimicrobial categorization. Approximately half of these strains were A. baumannii. All Acinetobacter species were 100% sensitive to colistin and to some extent to trimethoprim + sulfamethoxazole (74.5%). ICU-acquired pneumonia among patients over 60 years of age who spend prolong times at artificial ventilations made up the majority of the cases.