Dementia is one of the age-related diseases with the fastest increase in incidence. With the increasingly severe aging problem of the population, it further exacerbates the demand and burden of the healthcare system. Red blood cell distribution width (RDW) is an easily obtainable blood routine indicator that reflects the variability of red blood cell size. As an early marker of dementia risk, researches have shown an association between white matter hyperintensities (WMHs) and RDW. This article reviews the relationship between RDW and WMHs.