Objectives: Inflammation and coagulation perform a substantial act in the pathophysiology of COVID-19 cases. The systemic immune-inflammation index (SII) is a novel prognosis and inflamation index. In this study, we aimed to research the relation between SII and prognosis in COVID-19 patients. Methods: 315 cases (males, 136 ; females, 179 ; 63.2 ± 11.4 years) with positive PCR and lung tomography evidences compatible with COVID-19 pneumonia were recorded in the research. Patients were separated into 2 groups according to the mortality (Group 1; Surviving patients, Group 2; Ex patients). Clinical, demographic, and laboratory datas for whole patients were registered Laboratory datas were measured from blood parameters taken during hospitalization. The SII was calculated as “ SII = neutrophil count × platelet count / lymphocyte count ”. Results: The mean hospital stay of the patients is 12 (5-26) days. When the patients were assessment of according to clinical features, an important distinction was found between the two groups according to age, gender, cardiovascular disease, chronic renal failure, neurolvascular disease, and diabetes mellitus. When the patients were evaluated according to laboratory parameters, white blood cells, neutrophils, creatinine, D-Dimer, ferritin, CRP values were observed to be significantly higher in Group 2 patients than Group-1 patients. However, lymphocyte count, serum potassium level, albumin and calcium levels were observed to be significantly lower in Group-2 patients than in Group-1 patients. SII level was significantly higher in Group 2 patients than Group-1 patients (1813.4 ±118.7 vs 978.2 ± 93.1, p