Diabetes mellitus type 2 (T2DM) is considered to be an important risk factor for mild cognitive impairment (MCI) and subsequent Alzheimer's disease (AD). The majority of studies relating T2DM to MCI and AD were performed in North America. We investigated the potential impact of T2DM on the development of MCI and AD in the Interdisciplinary Longitudinal Study on Adult Development and Aging which involves a representative birth cohort of subjects born between 1930 and 1932 in Germany. Subjects received a thorough psycho-geriatric examination and neuropsychological testing; particular care was taken to exclude subjects with severe medical or neurological conditions sufficient to explain the cognitive deficits, or other major psychiatric disorders. When compared to healthy subjects (n=159), patients with MCI (n=108) or AD (n=26) showed a tendency towards increased prevalence rates for T2DM (17% vs. 23%; chi2=1.7, p=0.18). In both patients with MCI and controls, T2DM was associated with psychomotor slowing but not deficits in other cognitive domains typically involved in MCI. Our findings indicate that T2DM is involved in MCI and may aggravate the clinical picture as a concomitant factor.