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The prognostic value of pretreatment systemic immune-inflammation index (SII) in lung cancer has yet to be fully established.Relevant articles were obtained by performing a systematic search. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) were used to assess the relationship between SII index and overall survival (OS) in lung cancer; the OS was calculated from the time of cancer diagnosis to the date of death due to any cause or to the last date of follow-up.In total, 2786 patients with lung cancer from 7 studies were included in this meta-analysis. The median thresholds to define high SII was 640 (range 395.4–1600) in the analyzed studies. The pooled HR for OS was 1.77 (95% CI: 1.54–2.00, P < .001), suggesting that the patients with a high SII score had a worse OS. In addition, results from subgroup meta-analysis showed the significant prognostic significance of SII in lung cancer. Especially, the predictive value of SII was significant in the multivariable model for NSCLC (HR: 1.97, 95% CI: 1.69–2.25, P < .001; 5 studies, 1746 patients), and SCLC (HR: 1.38, 95% CI: 1.02–1.85, P < .001; 1 study, 919 patients).Our data suggest that high SII index indicates poor survival rate in lung cancer. Further researches are warranted to verify the significance of SII index in clinical practice.