OBJECTIVES: To clarify the usefulness of measuring serum carcinoembryonic antigen (CEA) preoperatively to detect patients who will have a poor outcome after surgery, and who cannot be selected by conventional staging modalities. METHODS: One hundred patients with adenocarcinoma of the lung underwent standard surgical procedures between 1994 and April 2001 at our institution. Preoperative staging was assessed according to the TNM classification of the International Union Against Cancer. The associations between preoperative serum CEA level and the postoperative recurrence or lymph node metastasis were examined. The serum CEA level was classified into two groups according to concentration of CEA level: low (normal) CEA (<or=5.0 ng/ml) and high CEA (>5.0 ng/ml). RESULTS: The high CEA level was associated with tumor relapse (P=0.01). According to the preoperative staging, the increased CEA was associated with tumor relapse only in stage C-IA (P=0.001). Stage C-IB and more advanced stages did not show an association between increased CEA and tumor relapse. In C-IA, risk for lymph node involvement was significantly higher in the high CEA group (4/9; 44.4%) than in the low CEA group (6/47; 12.8%, P=0.03). Furthermore, the rate of tumor relapse in C-IA-pN0 was significantly higher in the high CEA group (4 of the 5, 80%) than in the low CEA group (9 of the 41, 22.0%, P=0.018). The 5-year disease-free survival rate for patients with a high serum CEA level (N=9) was 22.2%, and 75.0% for patients with a normal CEA (N=47) level (P=0.0004). CONCLUSIONS: Increased serum CEA is an important predictive factor for poor outcome after surgery in early-stage (C-IA) lung adenocarcinoma.