Background/Aims: Type 2 diabetes mellitus (DM2) is associated with mild decrements in cognitive functioning, particularly in the elderly. It is often preceded by a 'prediabetic stage', characterized by the co-occurrence of insulin resistance and vascular risk factors, usually referred to as the metabolic syndrome. Cognitive decrements may already develop in these early stages. Methods: Cognitive functioning was compared cross-sectionally between DM2 patients (n = 64), patients with metabolic syndrome but without DM2 (n = 83) and control subjects (n = 100) participating in the prospective population-based Hoorn study. Participants performed an extensive neuropsychological examination. Vascular and metabolic determinants were recorded. Results: Both the DM2 group and the metabolic syndrome group performed worse than controls on the domains of information processing speed and attention and executive functioning (mean differences in z-scores 0.2-0.3, all p < 0.05). There were no significant differences in performance between the DM2 and metabolic syndrome group. None of the individual risk factors of the metabolic syndrome, measured at either the present or the previous examination, was a key determinant of cognitive functioning. Conclusion: These results show that DM2-associated cognitive decline may develop in early stages of the disease, possibly in relation to risk factors clustered in the metabolic syndrome.