OBJECTIVE: Iron has been suggested to play a role in the etiology of type 2 diabetes mellitus. Except for ferritin, evidence is sparse for other markers of iron metabolism which are regulated differently and might act through independent pathways. We therefore investigated the associations of serum ferritin, transferrin, soluble transferrin receptor (sTfR), transferrin saturation (TSAT), sTfR-to-log10ferritin (sTfR-F) index, and iron with impaired glucose metabolism (IGM / 'prediabetes'), type 2 diabetes, and four continuous glycemic traits. DESIGN AND METHODS: Data from 2,893 participants of the population-based Cooperative Health Research in the Region of Augsburg (KORA) F4 study (Germany) was investigated through regression analysis. The results were adjusted for socio-demographic, life-style and obesity measures as well as metabolic, inflammatory and other iron biomarkers following a step-wise approach. Non-linearity was tested by adding a non-linear spline component to the model. RESULTS: Ferritin and transferrin were positively associated with IGM (4th vs 1st sex-specific quartile: ferritin OR=2.08 [95%CI 1.43-3.04], transferrin OR=1.89 [1.32-2.70]), type 2 diabetes (ferritin OR=1.98 [1.22-3.22], transferrin OR=2.42 [1.54-3.81]) and fasting as well as 2-h glucose. TSAT (OR=0.55 [0.34-0.88]) and iron (OR=0.61 [0.38-0.97]) were inversely associated with type 2 diabetes, sTfR-F-index was inversely associated with IGM (OR=0.67 [0.48-0.95]). There was no strong evidence for non-linear relationships. CONCLUSIONS: The observed associations of several markers of iron metabolism with hyperglycemia and insulin resistance suggest that iron stores as well as iron-related metabolic pathways contribute to the pathogenesis of IGM and type 2 diabetes. Moreover, TSAT levels are decreased in type 2 diabetic patients.