Positron emission tomography (PET) is used for staging and response evaluation in primary gastric lymphoma (PGL). However, the implications of [(18)F]-2-fluoro-2-deoxy-D-glucose ((18)F-FDG) uptake in PGL at first diagnosis have not been reported. The relationship between (18)F-FDG uptake and the expression of facilitative glucose transporters (GLUTs), hexokinase II (HK II), and Ki67, as well as malignant potential in PGL, was assessed in this study. We analyzed 23 patients with PGL [nine with diffuse large B-cell lymphoma (DLBCL); seven with high-grade mucosa-associated lymphoid tissue (MALT) lymphoma; and seven with low-grade MALT lymphoma]. The expression levels of GLUT1, GLUT3, HK II, and Ki67 were evaluated according to the percentage of positive area determined by immunohistochemistry. Standardized uptake values correlated significantly with pathological malignant potentials (low-grade/high-grade MALT lymphoma and DLBCL: p = 0.001-0.002), Ki67 (p < 0.001), and GLUT1 expression (p = 0.02). We determined that (18)F-FDG uptake is related to GLUT1 expression and tumor histological grade as well as Ki67 in PGL.