Acinetobacter baumannii is an important opportunistic pathogen and responsible for a wide range of nosocomial infections including pneumonia, bacteremia, meningitis, urinary tract, burn and wound infections. These infections often occur in critically ill patients and usually after a relatively extended hospitalization period in intensive care units (ICUs) [1-3]. Previous studies in some hospitals highlighted the critical role of environmental contaminated inanimate objects and surfaces such as supply carts, floors, infusion pumps and ventilator touch pads by A. baumannii in the transmission of the infection to patients [4-6]. The extraordinary ability of A. baumannii to adapt to variable conditions like tolerance to desiccation and its remarkable ability to develop resistance to various antibiotics has led to the emergence of multidrug-resistant (MDR) A. baumannii strains which contribute to the persistence of these organisms in the hospital environment for extended periods of times [7-9]. Hospital outbreaks caused by A. baumannii are known to be associated with contaminated environments as well as healthcare personnel [6, 8-10]. An estimated 20% to 40% of nosocomial infections were attributed to cross-contamination via the hands of healthcare personnel, as a result of direct contact with patients or indirectly by contaminated inanimate surfaces [6]. Here, we investigated the potential cross-contamination of A. baumannii between the patients and their environment in EbneSina Hospital, Tehran, Iran. We also compared the antibiotic resistance patterns and the genetic fingerprints of the isolates obtained from various surfaces as well as the A. baumannii-infected patients. MATERIAL AND METHODS Bacterial Isolates. Forty-one non-duplicate specimens were collected from sputum, wounds, urine, and catheters of patients hospitalized in ICU, Post-ICU, and CCU of EbneSina Hospital, Tehran, Iran from June 2015 to April 2016. Also, 28 environmental samples were randomly collected from various inanimate objects and surfaces of all three wards (patients' beds, bedrails, bedside tables, patients' file covers, ventilators, supply carts, nursing station and wash basins). The patients' specimens were swabbed and streaked on MacConkey agar plates (Merck, Germany) and incubated at 37 o C overnight. For the collection of environmental samples, moistened cotton Introduction: Acinetobacter baumannii is one of the major causes of nosocomial infections. We investigated the presence of A. baumannii among patients and the environment in special care units of a hospital in Tehran, Iran. Methods: Sixty-nine nonduplicate clinical and environmental samples were collected from ICU, Post-ICU, and CCU in EbneSina Hospital (Tehran, Iran) from June 2015 to April 2016. The isolates were identified using standard biochemical tests, and their identity was confirmed by detection of blaoxa51 gene. Susceptibility to 14 antibiotics was determined by the disc diffusion method, and genetic fingerprinting of the isolates was performed by random amplified poly...