Introduction: The prevalence of neurocognitive disorders (NCDs) increases with age and is associated with cognitive impairment. Older patients with NCD admitted to the emergency department (ED) are readmitted after discharge to home more often than those without NCD. Comprehensive geriatric assessment (CGA) is effective for improving clinical outcomes in older patients; however, the usefulness of CGA for older patients with NCD admitted to the ED has not been investigated. The main objective of our study is to assess the effectiveness of a geriatric emergency medicine unit (GEMU) for elderly patients with NCD admitted to the ED. Methods: This historical cohort study included patients aged 75 years and older with NCD admitted to the ED of Limoges University Hospital in France over a 4-year period. We compared patients treated in our hospital’s GEMU, the MUPA unit (exposed group), and patients who received standard care by emergency physicians (control group). The primary end point was the incidence of 30-day readmissions. Results: The study included 801 patients admitted to the ED between January 1, 2015, and December 31, 2018 (400 in the exposed group). Of those, 72.5% were female, and the mean age was 87 ± 5 years. After adjusting for confounding factors, the 30-day readmission rate was significantly associated with the MUPA unit intervention. Conclusion: CGA in a GEMU improved health outcomes in elderly patients with NCD in the ED. We recommend that all EDs include a geriatric team, such as the MUPA unit, to treat all patients with NCD admitted to the ED.