Background: Numerous genetic changes are associated with metastasis and invasion of cancer cells. To identify differentially expressed invasion-associated genes, we screened a panel of lung cancer cell lines (CL1-0, CL1-1, CL1-5, and CL1-5-F4 in order of increasing invasive activity) for such genes and selected one gene, collapsin response mediator protein-1 (CRMP-1), to characterize. Methods: We used a microarray containing 9600 gene sequences to assess gene expression in the cell panel and selected the differentially expressed CRMP-1 gene for further study. We confirmed the differential expression of CRMP-1 with northern and western blot analyses. After transfecting and overexpressing CRMP-1 in highly invasive CL1-5 cells, the cells were assessed morphologically and with an in vitro invasion assay. We used enhanced green fluorescent protein-tagged CRMP-1 and fluorescence microscopy to localize CRMP-1 intracellularly. CRMP-1 expression in 80 lung cancer specimens was determined by real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). All statistical tests were two-sided. Results: Expression of CRMP-1 was inversely associated with invasive activity in the cell panel, an observation confirmed by northern and western blot analyses. CRMP-1-transfected CL1-5 cells became rounded and had fewer filopodia and statistically significantly lower in vitro invasive activity than untransfected cells (all P<.001). During interphase, CRMP-1 protein was present uniformly throughout the cytoplasm and sometimes in the nucleus; during mitosis, CRMP-1 was associated with mitotic spindles, centrosomes, and the midbody (in late telophase). Real-time RT-PCR of lung cancer specimens showed that reduced expression of CRMP-1 was statistically significantly associated with advanced disease (stage III or IV; P = .010), lymph node metastasis (N1, N2, and N3; P = .043), early postoperative relapse (P = .030), and shorter survival (P = .016). Conclusions: CRMP-1 appears to be involved in cancer invasion and metastasis and may be an invasion-suppressor gene.