Objectives: Comorbidities represent a risk factor for adverse events in several critical illnesses. The aim of this study was to identify the relationship between the Charlson Comorbidity Index (CCI) with mortality and length of stay (LOS) in critically ill elderly patients. Methods: A retrospective analysis was made of patients admitted to our tertiary adult intensive care unit (ICU) between January 2015 and January 2016. The impact of comorbidity was evaluated with the CCI. Other required data were retrieved from the patients' follow-up records. Results: The study included a total of 251 patients. The mean age was 78.79 ± 6.70 years. The total mortality rate was 41.0%. The most common cause for admission was sepsis and acute respiratory failure (18.3% vs 18.3%). The median APACHE II score was significantly higher in non-survivors than survivors (31.