Introduction: Covid 19 disease is considered a common public health problem and one of the leading causes of death. The clinical feature of this disease is that thyroid hormone levels are considered to be critically important in demonstrating vital functions. The effect of hormone levels on vital functions was investigated. Material and method: The patients who were treated in the intensive care unit between March 2020-2021 were examined and written informed consent was obtained from the patients. The thyroid hormone levels of the patients in the intensive care units were compared statistically and its effect on clinically important values was examined. Results: A total of 204 patients were included in the study. Thyroid hormone levels and infection parameters of the patients admitted to the intensive care unit were compared with their clinical features. Free t3 and free t 4 levels were found to be effective on mortality. Conclusion: It was supported by our study that fT3 and fT4 levels were lower in the group of patients who lost their lives in patients with severely severe COVID-19 infection. It has been seen that these hormone levels can be shown as a mortality indicator in the COVID-19 patient group, and we believe that prospective analyzes with additional studies can be illuminating on the subject.