The aim of the study was to evaluate impact of the systemic immune-inflammation index (SII) on prognosis and survival within the International Metastatic Renal Cell Carcinoma Database Consortium (IMDC) score groups.The records of 187 patients with metastatic renal cell carcinoma (RCC) were reviewed retrospectively. The SII was calculated as follows: SII = Neutrophil × Platelet/Lymphocyte. The patients were categorized into 2 groups based on a median SII of 730 (×109 per 1 L) as SII low (<730) and SII high (≥730). The Kaplan-Meier method was used for survival analysis and a Cox regression model was utilized to determine independent predictors of survival.The median age was 61 years (range: 34-86 years). Kaplan-Meier tests revealed significant differences in survival between the SII-low and SII-high levels (27.0 vs. 12.0 months, respectively, p < 0.001). The Cox regression model revealed that SII was an independent prognostic factor. The implementation of the log-rank test in the IMDC groups according to the SII level provided the distinction of survival in the favorable group (SII low 49.0 months vs. SII high 11.0 months, p < 0.001), in the intermediate group (SII low 26.0 vs. SII high 15.0 months, p = 0.007), and in the poor group (SII low 19.0 vs. SII high 6.0 months, p = 0.019).The SII was an independent prognostic factor and provided significant differences in survival for the favorable, intermediate, and poor IMDC groups. Thus, the SII added to the IMDC score may be clinically beneficial in predicting survival.