AIMS: To investigate the expression of beta-catenin in non-small-cell lung cancer (NSCLC) and its clinical significance. METHODS: 101 patients were surgically treated for NSCLC by lobectomy or pneumectomy with systematic lymph node dissection. Follow up was available in all patients, ranging from 24 to 110 months. Immunostaining of tissue sections from primary tumours and (when present) their lymph node metastases was performed and evaluated using a monoclonal antibody against beta-catenin. Correlations were investigated between beta-catenin immunostaining in primary tumours and E-cadherin immunostaining (data available from a previous study), lymph node stage, and survival. RESULTS: There were significant correlations between scores for beta-catenin immunostaining and E-cadherin immunostaining in primary tumours (p = 0.007), and between the beta-catenin immunostaining score in primary tumours and in their lymph node metastases (p = 0.006). An inverse correlation was found between the beta-catenin immunostaining score in primary tumours and lymph node stage N0, N1, or N2 (p = 0.03). According to the Kaplan-Meier survival estimate, the level of beta-catenin expression in primary tumours was a statistically significant prognostic factor (p = 0.01). CONCLUSIONS: Reduced beta-catenin expression in surgically treated NSCLC is clearly associated with lymph node metastasis and an infavourable prognosis. The existence of a functional relation between E-cadherin and beta-catenin is supported by the results of this clinicopathological study.