Importance:Current attempts to gauge the acute care needs of patients with dementia have not effectively addressed the role of caregivers, despite their extensive involvement in decisions about acute care management. Objective:To determine whether caregiver depression is associated with increased use of the emergency department (ED) among patients with dementia. Design, Setting, and Participants:This longitudinal cohort study used data from the Care Ecosystem study, a randomized clinical trial examining telephone-based supportive care for patients with dementia and their caregivers. Patients were 45 years or older with any type of dementia. A total of 780 caregiver-patient dyads were enrolled from March 20, 2015, until February 28, 2017, and 663 dyads contributed baseline and 6-month data and were included in the analysis. Exposures:Caregiver depression (9-item Patient Health Questionnaire score of ≥10). Secondary analyses examined caregiver burden and self-efficacy. Main Outcomes and Measures:The primary outcome was the number of ED visits in a 6-month period. Results:Among the 663 caregivers (467 women and 196 men; mean [SD] age, 64.9 [11.8] years), 84 caregivers (12.7%) had depression at baseline. The mean incidence rate of ED visits was 0.9 per person-year. Rates of ED presentation were higher among dyads whose caregiver did vs did not have depression (1.5 vs 0.8 ED visits per person-year). In a Poisson regression model adjusting for patient age, sex, severity of dementia, number of comorbidities, and baseline ED use, as well as caregiver age and sex, caregiver depression continued to be associated with ED use, with a 73% increase in rates of ED use among dyads with caregivers with depression (adjusted incident rate ratio, 1.73; 95% CI, 1.30-2.30). Caregiver burden was associated with higher ED use in the unadjusted model, but this association did not reach statistical significance after adjustment (incident rate ratio, 1.19; 95% CI, 0.93-1.52). Caregiver self-efficacy was inversely proportional to the number of ED visits in the unadjusted and adjusted models (adjusted incident rate ratio, 0.96; 95% CI, 0.92-0.99). Conclusions and Relevance:Among patients with dementia, caregiver depression appears to be significantly associated with increased ED use, revealing a key caregiver vulnerability, which, if addressed with patient- and caregiver-centered dementia care, could improve health outcomes and lower costs for this high-risk population.