S100A4 has been implicated in the malignant phenotype of tumor cells, including cell motility, but the biological function is hardly known. A recent study suggests that S100A4-induced invasiveness in malignant tumor cells is partially caused by down-regulation of E-cadherin. To clarify the clinical significance of S100A4 and its association with E-cadherin-mediated cell-to-cell adhesion system, we examined their protein expressions in non-small cell lung cancer (NSCLC) specimens using immunohistochemical techniques. Expression of S100A4 was observed in 81 (60%) of 135 NSCLCs and correlated with progression of the pathological T factor (p<0.001), lymph node metastasis (p<0.005), and poor survival (p<0.05). Reduced expression of E-cadherin, alpha-catenin, and beta-catenin was observed in 64% (87 of 135), 50% (43 of 86), and 58% (50 of 86) of the specimens tested, respectively. The expression of E-cadherin closely correlated with differentiation and inversely with that of S100A4. Among these adhesion-associated molecules we found that alpha-catenin appeared to reflect most strikingly the presence of lymph node metastasis and the short survival periods of NSCLC patients. Furthermore, patients who showed S100A4-positive/alpha-catenin-negative expression had a significantly shorter survival than the patients with S100A4-negative/alpha-catenin-positive expression. These results indicate that S100A4, as well as alpha-catenin, plays a role in the progression and metastasis of NSCLCs and that simultaneous immunohistochemical detection of their expression may be useful to define a subpopulation of lung cancer patients with a possible poor prognosis.