Background/Objectives: We examined the association between dietary intake and blood concentrations of one-carbon metabolism (OCM)-related nutrients in the European Prospective Investigation into Cancer and Nutrition (EPIC). Methods: Blood concentrations and dietary intake of the vitamins riboflavin (B2), Pyridoxal 5′-phosphate (PLP and B6), folate (B9), B12, and methionine, concentrations of homocysteine, and dietary intake of betaine, choline, and cysteine were pooled from 16,267 participants in nine EPIC nested case–control studies. Correlation analyses between dietary intakes and blood concentrations were carried out. Principal component (PC) analysis identified latent factors in the two sets of measurements. Results: Pearson correlations between dietary intakes and blood concentrations ranged from 0.08 for methionine to 0.12 for vitamin B2, 0.15 for vitamin B12, 0.17 for vitamin B6, and 0.19 for folate. Individual dietary intakes showed higher correlations (ranging from −0.14 to 0.82) compared to individual blood concentrations (from −0.31 to 0.29). Correlations did not vary by smoking status, case–control status, or vitamin supplement use. The first PC of dietary intakes was mostly associated with methionine, vitamin B12, cysteine, and choline, while the first PC of blood concentrations was associated with folate and vitamin B6. Conclusions: Within this large European study, we found weak to moderate associations between dietary intakes and concentrations of OCM-related nutrients.