Introduction: We aimed to investigate readmission risks following infections in dementia, identify the types of infections behind the risks, and highlight the reasons for readmissions. Methods: Acute inpatient hospital admissions for infections in Danish residents were included from 1 January 2000, or age 65 years. Primary outcomes were 7-day readmissions risk ratios (RRs; risk following infection index admissions of people with dementia relative to those without dementia), risks by infection site, and reasons for readmission. Secondary outcomes were 30- and 90-day readmission risks. Competing risk of death was estimated. Results: Seven-day readmission RR was increased in all age groups and was highest in the youngest patients (women RR: 1.41, 95% confidence interval [CI] 1.26–1.58; men RR: 1.28, 95% CI 1.16–1.40). RRs decreased with increasing age and longer follow-up. The most notable common readmissions were for infections and dehydration in dementia. Conclusions: We conclude that there is a substantially increased readmission risk in people with dementia than in those without dementia, particularly within 7 days, and for the youngest in the cohort. Readmission risks were higher for infection index admissions than for admissions for causes other than infection, and readmissions were mostly due to infections. Our findings highlight the burden of infections in people with dementia and call for in-depth investigations of determinants related to readmission risks, to inform public policy and identify avenues for interventions that can decrease or prevent potentially avoidable readmissions.