© 2020 by Turkish Society of Medical and Surgical Intensive Care Medicine.Objective: Hematological malignancies (HM) are the cause of many deaths worldwide and the incidence is increasing day by day. New treatment models increase remission rates; but complications that require intensive care unit (ICU) are also increasing. The aim of this study was to investigate the effect of The National Early Warning System Score (NEWSS) on ICU mortality in HM patients. Methods: This study was performed prospectively in the medical ICU. Patients transferred from hematology ward to the medical ICU were included in the study. NEWSS was calculated at the hematology ward before patients admitted to the ICU. Results: A total of 91 patients were enrolled in the study with a median (IQR) age of 55 (29) years. The median (IQR) NEWSS was 8 (3). Independent risk factors for ICU mortality were requirement of renal replacement therapy (P= 0.008), high Sequential Organ Failure Assessment (SOFA) score (P=0.002), development of Acute Respiratory Distress Syndrome (ARDS) (P=0.005). ICU mortality rate was 62%. Conclusion: Requirement of renal replacement therapy, high SOFA score and development of ARDS were important risk factors for ICU mortality in HM patients. The NEWSS was not found as a risk factor for ICU mortality in HM patients.