Mortality of healthcare-associated Acinetobacter baumannii bacteremia can be 50-60% in intensive care units (ICUs). We aimed to determine the risk factors for 28-day mortality in patients with sepsis due to A. baumannii bacteremia during their ICU follow-up. Demographic characteristics, disease severity scores on admission and bacteremia day (BD), resistance status, invasive interventions, and laboratory values showing the infection and severity of the BD, were compared between groups with and without mortality as a retrospective cohort study in the ICU of a tertiary hospital. Of a total of 2411 patients, there were 192 cases of bacteremia. After applying the exclusion criteria, 39 patients were recruited for the study, 25 of whom died (mortality rate 64.1%). Higher age, Simplified Acute Physiology Score II (SAPS II) on admission and high Sequential Organ Failure Assessment Score (SOFA), Red Blood Cell Distribution Width (RDW) (p < 0.001), and C-Reactive Protein (CRP) (p = 0.002) on the BD and invasive intervention in follow-up were associated with mortality. When CRP and RDW were both positive, sensitivity was 72%, specificity was 100%, negative predictive value was 33%, and positive predictive value was 100% for the 28-day mortality after BD. Based on multivariate analysis, CRP and RDW values on the BD were independent risk factors for mortality. It is critical to monitor SOFA, RDW, and CRP values in older ICU patients with SAPS II scores and who undergo invasive intervention in follow-up. Increases in these parameters may indicate bacteremia with high mortality due to A. baumannii.