Recently, by using differential display on specimens of non-small cell lung cancer (NSCLC), we detected overexpression of dihydrodiol dehydrogenase (DDH) that was rarely expressed in the corresponding normal lung tissue. DDH overexpression was correlated with poor prognosis of patients with advanced NSCLC. Because DDH could metabolize polycyclic aromatic hydrocarbons (PAH) in the liver, DDH overexpression in NSCLC would suggest an association with carcinogenesis and disease progression. In this study, we investigated DDH expression in 103 patients with resected stage I NSCLC. Expression of DDH was detected by using immunohistochemistry. Relation between DDH expression and clinicopathological parameter (age, gender, smoking habit, tumor status, histological type, cell differentiation, local recurrence, distant metastasis or survival) was analyzed by statistical analysis. DDH overexpression was detected in 39 (37.9%) of 103 pathological sections. Frequency of DDH overexpression was significantly higher in male patients (p=0.043) and patients with squamous cell carcinoma (p<0.005). Among 103 patients, 14 patients had local recurrence and 28 patients had distant metastasis during follow-up examination. The 5-year survival rate of these patients was poorer than those who did not have local recurrence or distant metastasis (both were p<0.005, respectively). Although patients with low DDH expression had more favorable outcome than those with DDH overexpression, in terms of survival rate no statistical significance was detected (p=0.889). The results suggest that DDH expression may serve as an early but not prognostic biomarker for patients with resectable stage I NSCLC.