Our objective was to clarify the efficacy of UFT administration after the complete resection of non-small cell lung cancer (NSCLC) at a single-center institution, avoiding the biases produced by interinstitutional differences. A total of 30 patients who underwent the complete resection of NSCLC at our hospital between 1987 and 2001 were randomly assigned to a control group or to a UFT group (400 mg/day for 2 years). Thirteen patients were assigned to the control group and 17 patients were assigned to the UFT group. The overall survival rate, disease-free survival rate, patient compliance and adverse effect of the UFT treatment were then analyzed. The overall survival and disease-free survival rates of the UFT group were superior to those of the control group. Four patients in the UFT group received medication for 24 months and 14 patients were treated for more than 3 months. No severe adverse effects were observed. Seven patients suffered a relapse in the control group. Two patients suffered a relapse in the UFT group, but the relapse occurred after the discontinuation of UFT administration. We conclude that the administration of UFT as an adjuvant therapy prolonged the overall survival and disease-free survival rates of patients after the resection of NSCLC in a small study performed at a single institution. Interinstitutional differences, particularly operating procedures, should be carefully considered when performing large multicenter clinical studies.