Background Dementia affects a large and growing number of older adults in the United States. The monetary costs attributable to dementia are likely to be similarly large and to continue to increase. Methods In a subsample (856 persons) of the population in the Health and Retirement Study (HRS), a nationally representative longitudinal study of older adults, the diagnosis of dementia was determined with the use of a detailed in-home cognitive assessment that was 3 to 4 hours in duration and a review by an expert panel. We then imputed cognitive status to the full HRS sample (10,903 persons, 31,936 person-years) on the basis of measures of cognitive and functional status available for all HRS respondents, thereby identifying persons in the larger sample with a high probability of dementia. The market costs associated with care for persons with dementia were determined on the basis of self-reported out-of-pocket spending and the utilization of nursing home care; Medicare claims data were used to identify costs paid by Medicare. Hours of informal (unpaid) care were valued either as the cost of equivalent formal (paid) care or as the estimated wages forgone by informal caregivers. Results The estimated prevalence of dementia among persons older than 70 years of age in the United States in 2010 was 14.7%. The yearly monetary cost per person that was attributable to dementia was either 56,290(95%confidenceintervalCI, 42,746 to 69,834)or 41,689 (95% CI, 31,017to 52,362), depending on the method used to value informal care. These individual costs suggest that the total monetary cost of dementia in 2010 was between 157billionand 215 billion. Medicare paid approximately 11billionofthiscost.ConclusionsDementiarepresentsasubstantialfinancialburdenonsociety,onethatissimilartothefinancialburdenofheartdiseaseandcancer.(FundedbytheNationalInstituteonAging.)