OBJECTIVE-Type 2 diabetes in midlife or late life increases the risk of Alzheimer disease (AD), and type 1 diabetes has been associated with a higher risk of detrimental cognitive outcomes, although studies from older adults are lacking. We investigated whether individuals with AD were more likely to have a history of diabetes than matched controls from the general aged population. RESEARCH DESIGN AND METHODS-Information on reimbursed diabetes medication (including both type 1 and 2 diabetes) of all Finnish individuals with reimbursed AD medication in 2005 (n = 28,093) and their AD-free control subjects during 1972-2005 was obtained from a special reimbursement register maintained by the Social Insurance Institute of Finland. RESULTS-The prevalence of diabetes was 11.4% in the whole study population, 10.7% (n = 3,012) among control subjects, and 12.0% (n = 3,372) among AD case subjects. People with AD were more likely to have diabetes than matched control subjects (unadjusted OR 1.14 [95% CI 1.08-1.20]), even after adjusting for cardiovascular diseases (OR 1.31 [1.22-1.41]). The associations were stronger with diabetes diagnosed at midlife (adjusted OR 1.60 [1.34-1.84] and 1.25 [1.16-1.36] for midlife and late-life diabetes, respectively). CONCLUSIONS-Individuals with clinically verified AD are more likely to have a history of clinically verified and medically treated diabetes than the general aged population, although the difference is small.