Introduction: The irrational use of antimicrobial drugs around the globe is an increasing clinical problem. Bacteria Acinetobacter baumannii has frequently shown increasing antimicrobial resistance over the past decade. Current research has shown that the most common cause of secondary infection and the most antibiotic-resistant bacteria in patients suffering from COVID-19, was the Acinetobacter baumannii bacterium. Aim: To examine the differences in the occurrence of the bacterium Acinetobacter baumannii in the blood culture of patients with COVID-19 and those who did not have COVID-19, and to determine the resistance of the bacterium Acinetobacter baumannii to antibiotics in patients treated against infection before the COVID-19 pandemic in relation to COVID-19 patients treated against the Acinetobacter baumannii co-infection at the University hospital Dubrava. Methods: A retrospective study analyzed laboratory findings of patients with isolated Acinetobacter baumannii in blood samples from January 1, 2018, to April 1, 2022, using descriptive and inferential statistics. Results: Records of 238 patients who underwent treatment for Acinetobacter baumannii bloodstream infection at Dubrava Hospital were analyzed. The observed periods showed no gender disparity in Acinetobacter baumannii infections, despite several studies suggesting a higher prevalence in males. During the pandemic, patients who were co-infected with COVID-19 and Acinetobacter baumannii had significantly longer hospitalization stays in Intensive Care Units compared to patients without COVID-19 but infected with Acinetobacter baumannii. During the COVID-19 pandemic, the resistance of Acinetobacter baumannii to the group of aminglycoside antibiotics - gentamicin and amikacin - increased, while for the antibiotics ampicillin + sulbactam and colistin, no statistically significant difference in the resistance of the isolates compared to the time before the COVID-19 pandemic was found. Conclusion: Co-infection with Acinetobacter baumannii has important implications for those suffering from COVID-19 as these patients were hospitalized longer in Intensive Care Units than patients without a COVID-19 infection. It was also observed that the resistance of the isolated strain of Acinetobacter baumannii to the antibiotics gentamicin and amikacin increased in patients who were sick with COVID-19 and at the same time had co-infection with the bacterium Acinetobacter baumannii.