The purpose of this prospective study is to determine the relative incidence of Alzheimer's disease in patients treated for at least three years, with sulodexide (n = 46, 76.48 ± 7.02 years old) or acenocoumarol (n = 47, 78.21 ± 6.66 years old) in order to prevent primary and secondary venous thromboembolism and atherothrombotic disease. In the sulodexide group, there was an apparent prevention of cognitive and behavioural impairment (relative incidence: 2.02) compared with acenocoumarol group (relative incidence: 4.86). The favourable results in sulodexide group may be related to their pharmacodynamic actions of inhibition of PAI-1, which may interfere with the pathogenesis of Alzheimer's disease, and to the role of glutathione and PAI-1 in the β-amyloid system in the brain.