Acinetobacter is a genus of bacteria which was not definitively established until 1971(Asia et al., 2003),This genus has undergone significant taxonomic alterations over the past 30 years. While there are many types of its species, the one which accounts for most reported infections is Acinetobacter baumannii, which has emerged as one of the most distributing pathogens for health care institutions globally. (Peleg, Seifert and Paterson, 2008)Acinetobacter species are gram-negative, nonfermentative, non-sporeforming, nonmotile, aerobic organisms. However, they can be gram-variable and appear gram-positive on initial gram stain. Morphologic features may differ depending on the growth phase, resulting in a rod-shaped appearance during rapid growth then a coccobacillary appearance during the stationary phase.(Asia et al., 2003; Kuo et al., 2012). The organism is able to survive under wide range of environmental conditions; in nature, it can easily grow in water and soil. It has also been isolated from food including hospital food and hospital equipment’s such as ventilator equipment, suctioning equipment, infusion pumps, sinks, pillows, mattresses, tap water and other sources.(Paterson, 2006; Perez et al., 2007; Zumla, 2010) It’s ability to chronically colonize rapidly can cause outbreaks which are hard to put an end to and set a challenge to infection control(Kuo et al., 2012) besides its effect on health care economics, as a study showed that treatment of such an infection can cost about $40,000 to cover a single patient case(Abd-Elmonsef, Elsharawy and Abd-Elsalam, 2017) Another study found that patients with Carbapenem resistant Acinetobacter Baumannii (CRAB) have higher total cost of hospitalization in the USA compared with patients having Carbapenem sensitive Acinetobacter Baumannii (CSAB);adjusted cost was US$ 11,359 versus US$ 7049; (p <0.001) In addition ,cost of antimicrobial medications have contributed to the higher cost in patients with CRAB.(Lemos et al., 2014) Acinetobacter Bumannii can cause multiple infections in the human body such as skin, soft tissues, blood, urinary tract, respiratory tract and orthopedic infections.(Asia et al., 2003)The respiratory tract is an important site of colonization and it's the most frequent site of infection especially pneumonia.(Asia et al., 2003)(Glew, Moellering and Kunz, 1977) Rates of colonization increases during ICU stays and as a result high prevalence of hospital acquired pneumonia.(Peacock et al., 1988)(Ayats et al., 1997)(Asia et al., 2003) One study in Riyadh suggested that the most common pathogen associates with HAP and VAP among ICU patients was Acinetobacter Baumannii (23.9%).(El-saed et al., 2013)This increased rate of pneumonia infection can be attributed to multiple prognostic factors such as; Recipients of mechanical ventilation may be prone to get infected with Acinetobacter Bumannii(Maragakis and Perl, 2008)(Kwon et al., 2007)(Alghaithy et al., 2012)(Young, Sabel and Price, 2007), prolonged length of hospitalization or transfer from another hospital, exposure to intensive care unit(Liu et al., 2015a)(Bercault and Boulain, 2001), surgical and postsurgical patients are at high risk to Acinetobacter baumannii infection due to suppressed immunity(Gowda, 2014)(Alghaithy et al., 2012),Invasive procedures.(Cisneros and Rodríguez-Baño, 2002)(Lee and Lee, 2016)(Clark, Zhanel and Lynch, 2016) Comorbidities and underlying diseases e.g.: COPD , cardiac diseases (Chang et al., 2011), and high APACHE score.(Lee et al., 2017) In addition, broad spectrum antibiotics use and delay in the administration of appropriate antibiotic therapy could increase the rate of infection(Calhoun, Murray and Manring, 2008)(Clark, Zhanel and Lynch, 2016)(Kwon et al., 2007)(Liu et al., 2015b)Multiple studies emphasized that ventilator associated pneumonia (VAP) caused by Acinetobacter baumannii has contributed to high risk of mortality rate.(El-saed et al., 2013)(Sileem, Said and Meleha, 2017)Some studies state that due to antibiotics resistance specifically carbapenem-resistant (CPR) mortality rates have increased from 20% to 50% along with increased hospitalization and ICU length of stay(Clark, Zhanel and Lynch, 2016; Garnacho-montero et al., 2016)However, the extremely drug resistant Acinetobacter baumannii (XDRAB) which defined as resistance to all available antibiotic except; colistien and tigacyclin is more predominant (67%), comparing to multidrug resistant Acinetobacter baumannii (MDRAB) (33%) which have resistant to two or three classes of antibiotics (Kuo et al., 2012)The only study conducted in the eastern province in Saudi Arabia in terms of resistance prevalence of Acinetobacter Baumannii was in Alahsaa, which they found a huge increase in the resistance pattern in 2010 and 2011 against multiple commonly used antibiotics such as: carbapenems, cephalosporin, piperacillin/tazobactam..etc (Ahmed et al., 2015) Since there are locally limited studies on this topic in the eastern province in Saudi Arabia, this study aims to provide an extensive information regarding the prognostic factors which predispose the patients to this infection and try to investigate the most effective drug regimen was at king Fahad university hospital in eastern province – Saudi Arabia for such patients.