KRAS gene mutations occur in approximately 40% of colorectal cancers (CRCs) and are associated with resistance to anti-epidermal growth factor receptor antibody therapy. We previously demonstrated that F-18-FDG accumulation in PET was significantly higher in CRCs with mutated KRAS than in those with wild-type KRAS in a clinical setting. Here, we investigated the mechanisms by which mutated KRAS increased F-18-FDG accumulation. Methods: Using paired isogenic human CRC cell lines that differ only in the mutational status of the KRAS gene, we measured F-18-FDG accumulation in these cells in vitro and in vivo. We also investigated the roles of proteins that have a function in F-18-FDG accumulation. Finally, we examined the relationship among mutated KRAS, hypoxia-inducible factor 1 alpha (HIF-1 alpha), and maximum standardized uptake value with 51 clinical CRC samples. Results: In the in vitro experiments, F-18-FDG accumulation was significantly higher in KRAS-mutant cells than in wild-type controls under normoxic conditions. The expression levels of glucose transporter 1 (GLUT1) and hexokinase type 2 (HK2) were higher in KRAS-mutant cells, and F-18-FDG accumulation was decreased by knockdown of GLUT1. Hypoxic induction of HIF-1 alpha was higher in KRAS-mutant cells than in wild-type controls; in turn, elevated HIF-1a resulted in higher GLUT1 expression and F-18-FDG accumulation. In addition, HIF-1 alpha knockdown decreased F-18-FDG accumulation under hypoxic conditions only in the KRAS-mutant cells. Small-animal PET scans showed in vivo F-18-FDG accumulation to be significantly higher in xenografts with mutated KRAS than in those with wild-type KRAS. The immunohistochemistry of these xenograft tumors showed that staining of GLUT1 was consistent with that of HIF-1 alpha and pimonidazole. In a retrospective analysis of clinical samples, KRAS mutation exhibited a significantly positive correlation with expressions of GLUT1 and HIF-1 alpha and with maximum standardized uptake value. Conclusion: Mutated KRAS caused higher F-18-FDG accumulation possibly by upregulation of GLUT1; moreover, HIF-1 alpha additively increased F-18-FDG accumulation in hypoxic lesions. F-18-FDG PET might be useful for predicting the KRAS status noninvasively.