Matrix metalloproteinase (MMP)-9 is an endopeptidase that digests basement membrane type IV collagen. Enhanced expression has been related to tumor progression both in vitro and in vivo. The control of MMP transcription is complex, but recently, epidermal growth factor receptor (EGFR) expression has been implicated in up-regulation of MMP-9 in tumor cells in vitro. Our objective was to evaluate the relationship between MMP-9 and EGFR expression in non-small cell lung cancer (NSCLC) and to assess the impact of expression on clinicopathological parameters and survival. This is a retrospective study of 169 patients who underwent resection for stage I-IIIa NSCLC with a postoperative survival >60 days. Minimum follow-up was 2 years. Standard avidin-biotin complex immunohistochemistry was performed on 4-microm paraffin-embedded sections from the tumor periphery using monoclonal antibodies to EGFR and MMP-9. MMP-9 was expressed in the tumor cells of 88 of 169 (52%) cases. EGFR expression was found in 94 of 169 (56%) cases [membranous, 55 of 169 (33%); cytoplasmic, 39 of 169 (23%)]. MMP-9 expression was associated with poor outcome in univariate (P = 0.0023) and multivariate (P = 0.027) analysis. Membranous, cytoplasmic, and overall EGFR expression were not associated with outcome (P = 0.13, 0.99, and 0.17, respectively). MMP-9 expression showed a strong correlation with EGFR expression (P < 0.0001) and EGFR membranous expression (P = 0.002) but not with cytoplasmic EGFR expression (P = 0.18). Co-expression of MMP-9 and EGFR (37%) conferred a worse prognosis (P = 0.0001). Subset analysis revealed only MMP-9 and membranous EGFR co-expression (22%) was associated with poor outcome (P = 0.0019). Our results show that a significant proportion of NSCLC tumors co-express MMP-9 and EGFR. The co-expression of these markers confers a poor prognosis. This finding suggests that EGFR signaling pathway may play an important role in the invasive behavior of NSCLC via specific up-regulation of MMP-9.