BACKGROUND AND OBJECTIVE Significant factors in the prognosis of p53 status in non-small cell lung cancer (NSCLC) remain controversial; some clinical studies have documented that p53 abnormality is a significant factor in predicting poor prognosis, and others failed. In the present study, we examined whether or not adjuvant therapy may influence the prognostic significance. METHODS 217 patients with pathologic stage I disease were reviewed. As postoperative adjuvant therapy, UFT, an oral 5-fluorouracil derivative, was administered to 73 patients; p53 status was determined immunohistochemically. RESULTS The 5-year survival rate for tumor with aberrant p53 expression was 66.4 %--significantly lower than that for tumor without aberrant p53 expression (79.7%, p = 0.023). The prognostic significance of p53 status was enhanced in patients who received UFT; 5-year survival rates for tumor with and without aberrant p53 expression were 68.8 and 94.7%, respectively (p = 0.002). In patients who did not receive UFT, the difference did not reach statistical significance (5-year survival rates: 65.5 and 71.5%, respectively; p = 0.267). CONCLUSIONS This study demonstrates that postoperative survival is improved by UFT administration in patients with normal p53 function, but not in those without normal p53 function.