Matrix metalloproteinases (MMPs) might be involved in invasion and metastasis of tumors by degrading extracellular matrix (ECM) and basement membrane (BM). The 5A or 6A single nucleotide polymorphism (SNP) at the -1 171 bp site of promoter region of MMP-3 may modify the transcription and local expression of MMP-3. This study was to investigate correlation of the MMP-3 SNP with genetic susceptibility and lymph node metastasis of non-small cell lung cancer (NSCLC).