ObjectiveTo explore the association of pretreatment hyponatremia with clinicopathological and prognostic characteristics of non-small cell lung cancer (NSCLC) patients. MethodsThe PubMed, EMbase, Web of Science, VIP, CNKI and WanFang databases were searched from the inception to July 12, 2021 for relevant literatures. The quality of included studies was assessed by the Newcastle-Ottawa Scale (NOS) score. The relative risk (RR) and hazard ratio (HR) with 95% confidence interval (CI) were combined to assess the relationship between pretreatment hyponatremia and clinicopathological and prognostic characteristics. The prognostic indicators included the overall survival (OS) and progression-free survival (PFS). All statistical analysis was conducted by the STATA 15.0 software. ResultsA total of 10 high-quality studies (NOS score≥6 points) involving 10 045 patients were enrolled and all participants were from Asian or European regions. The pooled results demonstrated that male [RR=1.18, 95%CI (1.02, 1.36), P=0.026], non-adenocarcinoma [RR=0.86, 95%CI (0.81, 0.91), P＜0.001] and TNM Ⅲ-Ⅳ stage [RR=1.17, 95%CI (1.12, 1.21), P＜0.001] patients were more likely to experience hyponatremia. Besides, pretreatment hyponatremia was significantly related to worse OS [HR=1.83, 95%CI (1.53, 2.19), P＜0.001] and PFS [HR=1.54, 95%CI (1.02, 2.34), P=0.040]. Pretreatment hyponatremia was a risk factor for poor prognosis of NSCLC patients. ConclusionMale, non-adenocarcinoma and advance stage NSCLC patients are more likely to experience hyponatremia. Meanwhile, the pretreatment sodium level can be applied as one of the prognostic evaluation indicators in NSCLC and patients with hyponatremia are more likely to have poor survival. However, more researches are still needed to verify above findings.