Aim: In this study, we aimed to investigate the lactate value and lactate clearance (LC) at the time of presentation to the emergency department and within the first two hours in predicting mortality in patients diagnosed with diabetic ketoacidosis (DKA). Material and Methods: This retrospectively and observationally planned cohort study was conducted with patients with DKA who presented to the hospital between January 2021 and December 2022. The patients' demographic characteristics, biochemistry, hemogram, and blood gas results at the time of presentation, second-hour lactate value, and outcome parameters were recorded. Then, LC was calculated for each patient. The patients were divided into groups according to the mortality status and the length of hospital stay. The groups were compared in terms of age, blood gas pH, osmolarity, glucose level, lactate level at presentation and at the second hour, LC, and bicarbonate, blood urea nitrogen, potassium levels, length of stay in hospital, intensive care unit admission, inotropic agent requirement, invasive mechanical ventilation requirement and mortality. Results: The overall mortality rate was 15.6% (16/102). Age, pH, osmolarity, bicarbonate and sodium levels, and second-hour lactate level significantly differed between the groups (Mann-Whitney U test, p<0.05). The cut-off and area under the curve values of LC were not significant in predicting mortality (p>0.05). Discussion: Among the patients with DKA who presented to the emergency department, age, the presence of comorbidities, glucose levels at presentation, admission and second-hour lactate values, pH, bicarbonate, potassium, and intensive care unit admission were useful in predicting mortality.