Pneumonia is a clinical condition that can increase oxidative stress and can cause hospitalization and intensive care unit (ICU) stay. Oxidative stress increases the production of pulmonary inflammatory mediators in the respiratory system, and this inflammatory process can cause DNA damage. This study aimed to determine the DNA damage levels of patients diagnosed with pneumonia and monitored in the ICU. From 50 patients and 30 healthy volunteers, 3 mL of blood was drawn, and DNA damage was determined using the Comet assay. Two slides were prepared for each sample, and 50 randomly selected cells from each slide were photographed using Zeiss Imager A1 fluorescence microscope and Axiocam Icc 1 camera. The photographs were analyzed using the OpenComet software and tail DNA percentage parameter was chosen to demonstrate DNA damage. The DNA damage of intubated, non-intubated, and all pneumonia patients were compared with the control group. DNA damage was 2.48 +/- 2.81 in the control group, 3.19 +/- 5.99 in the pneumonia group, 2.97 +/- 5.58 in intubated patients, and 3.50 +/- 6.32 in non-intubated patients. DNA damage was higher in all groups than in the control group (p < 0.001). However, the DNA damage of intubated patients was significantly lower than that of non-intubated patients (p < 0.001). As a result of the study, it was found that DNA damage decreased in patients who were intubated and received oxygen support.