Introduction: Sepsis and septic shock are the most serious clinical conditions in intensive care units with increased mortality rates. Efforts on improving treatment modalities and survival is still the most hot topic worldwide. One of the key points is finding out a reliable and cost-effective marker that can predict prognosis. The neutrophil-lymphocyte ratio (NLR) has been shown to be associated with prognosis in various clinical situations. The aim of this study was to investigate the relationship of NLR at admission and disease severity and 28-day mortality in sepsis and septic shock patients.