['Detection rates of gastric cancer in F-fluorodeoxyglucose (FDG)-PET depend on the histopathological characteristics of the primary tumor. To clarify this observation, FDG uptake in gastric carcinoma was analyzed by focusing on histopathology and on the expression of the glucose transporter (GLUT-1) in the primary tumor.', 'Thirty-five patients with the diagnosis of gastric cancer underwent FDG-PET with visual image analysis and measurement of maximum standardized uptake value (SUV(max)) before surgical treatment. Resected tumor samples were categorized according to Union internationale contre le cancer, WHO, and Laurén classification and tumor differentiation. GLUT-1 expression was graded semiquantitatively by immunohistochemistry. Statistical analysis was done for the correlation of histology, different classifications, and tumor grading with SUV(max) and GLUT-1 expression.', 'SUV(max) significantly correlated with histopathological classifications according to the WHO (P=0.009) and Laurén classification (P=0.034). Signet-ring cell carcinoma had a median SUV(max) of only 3.0 (range, 1.0-11.5). Median SUV(max) for papillary and tubular carcinoma was 7.8 (range, 1.8-14.4). In 21 (60%) cases, GLUT-1 expression in the primary tumor was positive. GLUT-1 expression correlated significantly with tumor differentiation (P=0.018) and the classification according to Laurén (P=0.023) and WHO (P<0.001). Thirteen (76%) of 17 signet-ring cell carcinoma cases did not show any GLUT-1 expression. SUV(max) in relation to GLUT-1 expression showed a significant correlation (P=0.002). For cases with detectable GLUT-1 expression the median SUV(max) was 6.9 (range, 2.3-14.1) versus a median of 3.1 (range, 1-8.8) for cases without GLUT-1 expression.'] Is variable 18F-fluorodeoxyglucose uptake in gastric cancer associated with different levels of GLUT-1 expression?