Purpose: The Int6 gene was originally identified as a common insertion site for the mouse mammary tumor virus in virally induced mouse mammary tumors. Recent studies indicate that Int6 is a multifaceted protein involved in the regulation of protein translation and degradation through binding with three complexes: the eukaryotic translation initiation factor 3, the proteasome regulatory lid, and the constitutive photomorphogenesis 9 signalosome. This study aimed to investigate the prognostic role of Int6 in a large series of stage I non-small cell lung cancers (NSCLC) patients with long-term follow-up.Experimental Design: We determined the methylation status of Int6 DNA by methylation-specific PCR and the steady-state levels of Int6 RNA by quantitative real-time reverse transcription-PCR in 101 NSCLCs and matched normal lung tissues.Results: In 27% of the tumors, Int6 RNA levels were reduced relative to normal tissue. In 85% of the tumors with reduced Int6 expression, the transcription promoter and first exon were hypermethylated, whereas only 4% of the tumors with elevated Int6 RNA levels were hypermethylated (P < 0.000001). Low levels of Int6 RNA were found a significant predictor of overall and disease-free survival (P = 0.0004 and P = 0.0020, respectively). A multivariate analysis confirmed that low Int6 expression was the only independent factor to predict poor prognosis, for both overall (P = 0.0006) and disease-free (P = 0.024) survival.Conclusions: Our results suggest that Int6 expression, evaluated by quantitative real-time PCR, may represent a new prognostic factor in patients with stage I NSCLC.