E-cadherin is a calcium-dependent, epithelial cell adhesion molecule whose reduced expression has been associated with tumor dedifferentiation and increased lymph node metastasis in clinical studies involving several carcinomas. In this study, 111 patients who had previously undergone complete resection and systematic mediastinal lymph node dissection for non-small cell lung cancer (NSCLC) were studied retrospectively. In the primary tumor, as well as in the lymph node metastases, E-cadherin expression was detected by immunohistochemistry using a monoclonal antibody (HECD-1; Takara, Otsu, Japan). There was a significant inverse correlation between E-cadherin expression and lymph node stage (Pearson correlation coefficient -0.52, p = 0.0001) as well as tumor differentiation (Pearson correlation coefficient -0.27, p = 0.005). Moreover, Kaplan and Meier survival estimates showed a significant correlation between E-cadherin expression and patient survival in log rank testing (p = 0.006). In the patient group with the highest proportion of E-cadherin positive tumor cells, 60% of the patients were still estimated to be alive at 36 mo, versus 32% of the patients in the group classified as showing negative E-cadherin expression. Our findings provide clinical evidence that reduced E-cadherin expression is associated with tumor dedifferentiation, increased lymphogenous metastasis and poor survival. It seems therefore that E-cadherin expression might be an important prognostic factor in NSCLC.