Positron emission tomography (PET) with (18)F-2-deoxy-2-fluoro-D-glucose (FDG) has been investigated as a means of detecting certain primary tumors and their metastatic disease in recent years. The aim of this study was to compare the performance of FDG-PET and operative assessment with formal pathologic staging. Altogether, 85 patients had undergone surgical treatment for gastric cancer with curative intent, with FDG-PET preoperatively. The results using FDG-PET were compared with those using computed tomography (CT); they were also correlated with the pathologic findings. For quantitative analysis, the regional tumor uptake was measured by the standard uptake value (SUV) using a region of interest technique. Using FDG-PET, the primary tumor was visualized in 75.2% of patients. A comparison of the FDG uptake and the clinicopathologic findings showed that there was a significant association between FDG uptake and the depth of invasion, the size of the tumor, and lymph node metastasis. FDG-PET scans had less accuracy for diagnosing locoregional lymph nodes than CT because of a significant lack of sensitivity (23.3% vs. 65.0%). The survival rate for patients with high FDG uptake (SUV > 4) was significantly lower than that for those with low FDG uptake (SUV < 4) ( p < 0.05). FDG-PET was successful in detecting the primary gastric cancer lesion but not for finding early-stage gastric cancers. Detection of nodal metastasis also was not possible by FDG-PET. However, FDG-PET appears to provide important additional information concerning the aggressiveness of the tumor and the prognosis in patients with gastric cancer.