Background: The risk of Alzheimer's disease (AD) is increased in type 2 diabetes (DM2). This increased risk has been attributed to vascular comorbidity, but other mechanisms, such as accelerated ageing of the brain, have also been implicated. Objective: To determine whether AD in patients with DM2 is associated with an increased occurrence of vascular lesions in the brain, by increased cerebral atrophy, or a combination of both. Methods: In total, 29 patients with AD and DM2 and 58 patients with AD and without DM2 were included in the study. Clinical characteristics were recorded, and a neuropsychological examination and magnetic resonance imaging (MRI) scan were performed. MRI scans were rated for cortical and subcortical atrophy, medial temporal lobe atrophy, white matter lesions, and infarcts. Results: The neuropsychological profiles of the two groups were identical. Patients with AD and DM2 had increased cortical atrophy on MRI (p<0.05) compared with the non-DM2 group. In addition, infarcts were more common (odds ratio 2.4; 95% CI 0.8 to 7.8), but this effect did not account for the increased atrophy. The other MR measures did not differ between the groups. Conclusion: The results suggest that non-vascular mechanisms, leading to increased cortical atrophy, are also involved in the increased risk of AD in DM2.