BACKGROUND: Although overall health and social care expenditures among persons with dementia are larger than for other diseases, the resource and cost implications of a comorbid diagnosis of dementia in acute hospitals in the U.S. are largely unknown. We estimate the difference in inpatient outcomes between similar hospital admissions for patients with and without comorbid dementia (CD). METHODS: Inpatient admissions, from the U.S. National Inpatient Sample (2016-2019), were stratified according to hospital characteristics and primary diagnosis (using ICD-10-CM codes), and entropy balanced within strata according to patient and hospital characteristics to create two comparable groups of admissions for patients (aged 65 years or older) with and without CD (a non-primary diagnosis of dementia). Generalized linear regression modeling was then used to estimate differences in length of stay (LOS), cost, absolute mortality risk and number of procedures between these two groups. RESULTS: The final sample consisted of 8,776,417 admissions, comprised of 1,013,879 admissions with and 7,762,538 without CD. CD was associated with on average 0.25 (95 % CI: 0.24-0.25) days longer LOS, 0.4 percentage points (CI: 0.37-0.42) higher absolute mortality risk, $1187 (CI: -1202 to -1171) lower inpatient costs and 0.21 (CI: -0.214 to -0.210) fewer procedures compared to similar patients without CD. CONCLUSION: Comorbid dementia is associated with longer LOS and higher mortality in acute hospitals but lower inpatient costs and fewer procedures. This highlights potential communication issues between dementia patients and hospital staff, with patients struggling to express their needs and staff lacking sufficient dementia training to address communication challenges.