Objectives. The aim was to determine whether red cells distribution width (RDW) in mechanically ventilated nonsurgical patients with a fatal outcome was significantly higher than in those who did not experience a fatal outcome during their stay in the intensive care unit and to establish the so-called cut-off value of RDW that best predicted death in those patients, with the highest sensitivity and specificity. Study design. Historical cohort study. Participants and methods. The research was conducted on 100 nonsurgical patients on mechanical ventilation in the Intensive Care Unit at the Department of Pulmonology and Intensive care for Internal Medicine patients within the Clinical Hospital Center Osijek in the period from January to June 2023. Patient data were collected from the hospital information system. Results. There was no significant difference in RDW between patients who survived and those who died. Hemodynamic instability as the reason for patient admission (P < 0.001) and the main diagnoses of patients (P = 0.018) showed statistically significant association with the poor survival outcome in the Intensive Care Unit. Patients older than 56 years and with higher concentrations of alkaline phosphatase (greater than 92 IU/L), urea (greater than 14.1 mmol/L), creatinine (greater than 98 μmol/L), C-reactive protein (greater than 84.4 mg/L), and procalcitonin (greater than 0.5 μg/L) were at higher risk of death in the Intensive Care Unit. Conclusion. RDW was not predictive of survival in nonsurgical patients who were mechanically ventilated. Despite its association with poor outcomes of survival in the Intensive Care Unit considering other conditions and studies similar to this one, our results contribute to the understanding that RDW is not a universal predictor of the worst outcome..