Solute carrier family 5 member A8 (SLC5A8) is a sodium-coupled transporter for several chemicals. The SLC5A8 gene has been reported to function as a tumor suppressor gene that contributes to carcinogenesis and tumor progression. The expression of SLC5A8 is silenced in colon neoplasia by hypermethylation of CpG-rich islands located in exon 1. In this study, we assessed the significance of aberrant methylation of the SLC5A8 gene as a prognostic factor for lung adenocarcinoma (AD).We analyzed the methylation levels of a consecutive series of 143 node-negative stage I and II lung AD samples using pyrosequencing.The methylation level of exon 1 in the SLC5A8 gene was significantly associated with poor prognosis in cases of node-negative stage I and II lung AD.Gene silencing of SLC5A8 by hypermethylation was associated with poor prognosis in cases of node-negative stage I and II lung AD.