Background: E-Cadherin is a subclass of the cadherin family that plays a major role in the maintenance of intercellular junctions in normal epithelium. Decreased expression of E-cadherin might be closely related to invasiveness and dedifferentiation in human cancers. This study is aimed at investigating the clinicopathological significance of E-cadherin expression and its impact on the prognosis in surgically resected non-small-cell lung cancer patients. Methods: Using immunohistochemical staining, the expression of E-cadherin was studied in 207 surgically resected lung cancer specimens from January 1990 through December 1994. The clinicopathological data and survival status were recorded and analysed against the E-cadherin expression level in each tumor. Results: E-cadherin expression was detected in 122 of the 207 lung tumors (59.0 %), and the expression was significantly lower in tumors with poor differentiation (p < 0.001), in tumors with vascular invasion (p < 0.05), and in tumors with direct invasion into surrounding structures (p < 0.01). There was no correlation between E-cadherin expression, and tumor stage and regional lymph-node metastasis.There was no significant difference in survival rate between higher (> 40 %) and lower (< 40 %) E-cadherin expression groups; however, in tumors 3 cm or less, a significant difference was found between higher and lower E-cadherin expressions (p < 0.0001). Conclusions: Underexpression of E-cadherin is associated with poor differentiation and invasiveness in NSCLC. In patients with small NSCLC (≤ 3 cm), higher E-cadherin expression (> 40 %) significantly had a favorable prognosis.