Background: Dementia is the fourth most common cause of death in developed countries. The relationship between plasma lipids and cognitive function is complex and controversial. Due to the increasing life expectancy of the population, there is an urgent need to control vascular risk factors and to identify therapies to prevent and treat both cognitive impairment and dementia. Here, we reviewed the effects of plasma lipids and statins on cognitive function. Data Sources: We searched the PubMed database for research articles published through November 2017 with key words includingplasma lipids, hyperlipidemia, hypercholesterolemia, statins, and cognition function.Study Selection: Articles were retrieved and reviewed to analyze the effects of plasma lipids and statins on cognitive function and the mechanisms underlying these effects. Results: Many studies have examined the relationship between plasma lipids and cognitive function, but no definitive conclusions can be drawn. The mechanisms involved may include blood-brain barrier injury, the influence on small blood vessels in the brain, the influence on amyloid deposition, and a neuroprotective effect. To date, most studies of statins and cognition have been observational, with few randomized controlled trials. Therefore, firm conclusions regarding whether mid- or long-term statin use affects cognition function and dementia remain elusive. However, increasing conc exists that statins may be a causative factor for cognitive problems. These adverse effects appear to be rare and likely represent a yet-to-be-defined vulnerability in susceptible individuals. Conclusions: The association between plasma lipids and cognition, the mechanism of the influence of plasma lipids on cognitive function, and the association between statins and cognitive function are complex issues and currently not fully understood. Future research aimed at identifying the mechanisms that underlie the effects of plasma lipids and statins on cognition will not only provide important insight into the causes and interdependencies of cognitive impairment and dementia, but also inspire novel strategies for treating and preventing these cognitive disorders.