Platelets play an important role in atherosclerosis, and increased platelet activation is associated with stroke. Stroke is an important risk factor for dementia, as approximately 25% of the patients are demented after stroke. In this review, we describe platelet activation studies in patients with stroke and with dementia. In addition, we review the few studies that have investigated the effect of antiplatelet medication such as aspirin and non-steroidal anti-inflammatory drugs on cognitive function and the occurrence of dementia. We conclude that further studies are needed to characterize the mechanisms and determinants of platelet activation in relation to the development of dementia. Furthermore, the efficacy and safety of antiplatelet intervention will have to be assessed in properly designed randomized trials.