We know that mortality had increased in diabetic patients with COVID-19 pneumonia. The aim of this study was to compare the mortality and inflammation parameters difference in critically ill COVID-19 patients according to their admission HbA1c levels and diabetes mellitus status. Secondary aim was to evaluate the effect of the first week hyperglycemic episode frequency on mortality. Critically ill COVID-19 patients who were tested for HbA1c levels on ICU admission were analyzed retrospectively. Of 218 COVID PCR(+) patients, 139 met the inclusion criteria in study period. The median age was 67 [57-76] years and 55(40%) of them were female. Seventy-six (55%) of the patients required invasive mechanical ventilation (IMV). The IMV requirement was higher in diabetic patients (p=0.01). When the groups were compared in terms of inflammatory parameters no significant difference was found except for admission and first week's highest fibrinogen levels (p=0.02 and p=0.03, respectively). In multivariate analysis, fibrinogen levels were not determined as a risk factor for mortality. Overall ICU mortality was 43% (60/139). In group-1 23 (37%), in group-2 27 (57%), and in group-3 10 (34%) patients had died. There was no statistically significant difference between groups in terms of mortality (p=0.05). Records of 96 (69%) patients revealed there were more than five glucose readings over 180mg/dL during the first week. Mortality was higher in patients with more frequently hyperglycemic recordings (p=0.03). There was no significant mortality and inflammatory parameters difference in patients with and without diabetes. However, more than five glucose readings over 180mg/dL during the first week were found with increased mortality.