PURPOSE: The prognostic significance of peri-operative serum carcinoembryonic antigen (CEA) and carbohydrate antigen (CA)19-9 determination in patients with gastric cancer has been controversial. This study was performed to evaluate the significance of CEA and CA19-9 as clinical predictors of prognosis. MATERIALS AND METHODS: The correlations between peri-operative serum CEA/CA19-9 levels and clinicopathologic factors were evaluated retrospectively in gastric cancer patients who had undergone curative surgery during the period from January 1995 to December 1998 at the Department of Surgery, Yonsei University College of Medicine. RESULTS: The positive rates for CEA and CA19-9 were 17.9% and 18.4%, respectively. The CEA positivity was related to the depth of invasion (P=0.040), lymph-node metastasis (P=0.000), and stage (P=0.001). The CA19-9 positivity was significantly related to the depth of invasion (P=0.000), lymph-node status (P=0.000), and stage (P=0.000). The positive rate of combined assay of pre-operative CEA and CA19-9 was 30.0%. There were statistically significant correlations with stage, depth of invasion, or degree of lymph- node metastasis in the combined assay. The survival rates according to the positivity of CEA and to the positivity of CA19-9 were clearly different (P=0.000). CONCLUSION: It should be stressed that even a simple blood test prior to surgery could be useful in establishing the depth of invasion, the status of lymph-node involvement, and the prognosis. For improved survival, an aggressive lymphadenectomy and adjuvant chemotherapy should be considered for patients with positive levels of pre-operative CA19- 9.