Dementia, a clinical syndrome affecting memory, thinking, and social abilities primarily caused by neurodegeneration, is becoming one of the greatest health and socioeconomic burdens in an aging society. The age-standardized prevalence of dementia for people aged 60 or older was 5-7% in most world regions, affecting 35.6 million in 2010. This number is expected to almost double every 20 years. Although aging is the greatest but non-modifiable risk factor, approximately 35% of the risk has been attributed to the combination of potentially modifiable risk factors including education, diet and lifestyle factors, psychiatric factors, and metabolic factors. Now there is ample evidence that people with glucose intolerance, insulin resistance and metabolic syndrome are at higher risk for cognitive impairment and dementia compared to age- and gender-matched controls. Meta-analyses and large-scaled pooled analyses demonstrate that diabetes is associated with an approximately 60-70% increased risk of all types of dementia. In this lecture, I’d like to demonstrate evidences on the associations of hyperglycemia, hypoglycemia, and glucose variability with cognitive dysfunction and dementia. Also, the underlying mechanism of this connection will be discussed.