Background: Vascular dementia (VaD) is the second most common dementing illness. Multiple risk factors are associated with VaD, but the individual contribution of each to disease onset and progression is unclear. We examined the relationship between diabetes mellitus type 2 (DM) and the clinical variables of VaD.Methods: Data from 593 patients evaluated between June, 2003 and June, 2008 for cognitive impairment were prospectively entered into a database. We retrospectively reviewed the charts of 63 patients who fit the NINDSAIREN criteria for VaD. The patients were divided into those with DM (VaDDM, n = 29) and those without DM(VaD, n = 34). The groups were compared with regard to multiple variables.Results: Patients with DM had a significantly earlier onset of VaD (71.9 ± 6.54 vs. 77.2 ± 6.03,p < 0.001), a faster rate of decline per year on the mini mental state examination (MMSE; 3.60 ± 1.82 vs. 2.54 ± 1.60 points, p = 0.02), and a greater prevalence of neuropsychiatric symptoms at the time of diagnosis (62% vs. 21%, p = 0.02).Conclusions: A history of premorbid DM was associated with an earlier onset and faster cognitive deterioration in VaD. Moreover, DM was associated with neuropsychiatric symptoms in patients with VaD. A larger study is needed to verify these associations. It will be important to investigate whether better glycemic control will mitigate the potential effects of DM on VaD.