INTRODUCTION Phenotypic characterization of the Acinetobacter genus bacteria through biochemical and microscopic tests is possible. Studies have shown that the isolates from health-care associated infections show high resistance to first-line antibiotics. OBJECTIVE To describe the resistance patterns of the A. baumannii isolates obtained in a health care institution, the phenotypic characteristics of the isolates, and the possible resistance mechanisms. MATERIALS AND METHODS A descriptive cross-sectional study was conducted with 28 reports of samples taken from patients hospitalized with infection by A. baumannii . Susceptibility testing for ceftazidime, cefepime, meropenem, amikacin, and ciprofloxacin was performed with the Vitek automated system and the susceptible, intermediate, and resistant classification was based on the protocol established by the Clinical and Laboratory Standards Institute for 2007. RESULTS The highest percentage of isolates corresponded to males (53.6 %), to the infectology ward (28.5 %), and to the month of September (21.4 %); the most frequent sample site were endotracheal secretions (53.6 %). From the profile patterns for susceptibility to antibiotics used, 13 phylotypes were obtained. CONCLUSION Acinetobacter baumannii is a pathogen resistant to multiple antimicrobial agents involved in outbreaks of health-care associated infections. The resistance profile patterns allow inferring that the possible resistance mechanisms present in the majority of the isolates are: Production of extended-spectrum b -lactamases, antibiotic modifying enzymes, and target site modification.