['Previous epidemiologic studies indicate that diabetes mellitus (DM) is associated with cognitive decline and an increased risk of developing Alzheimer disease (AD) in people who do not have dementia. However, little is known about the effect of DM on the rate of cognitive decline in established AD. Our objective was to determine whether DM influences the rate of cognitive decline in patients with AD.', 'A total of 608 patients with a probable diagnosis of AD and a Mini-Mental State Examination (MMSE) score between 10 and 26 were enrolled in a prospective multicenter study. Participants were followed up to 52 (mean 26) months. DM was assessed at baseline (history of DM or antidiabetic medication use). Cognitive function was assessed twice yearly with the MMSE.', 'Sixty-three participants (10.4%) had DM at baseline. In a mixed model adjusted for sex, age, educational level, dementia severity, cholinesterase inhibitor use, and vascular factors (hypertension, atrial fibrillation, coronary heart disease, and hypercholesterolemia), there were no differences between the groups in MMSE baseline scores (-0.75, p = 0.20), but cognitive decline was slower in the group with DM (0.38, p = 0.01).'] Is diabetes associated with a slower rate of cognitive decline in Alzheimer disease?