Increased levels of inflammatory markers have been found in association with the severity of coronary atherosclerosis. Systemic immuneinflammation index (SII), which is calculated by multiplying neutrophil and platelet counts and then dividing the result by the lymphocyte count, can also be used as a prognostic indicator in different cardiovascular diseases. In this study, we investigated SII levels and long-term mortality of patients with non-ST segment elevation myocardial infarction (NSTEMI).