Aim: The aim of the study was to evaluate the association of death within 8–30 days after discharge home from the emergency department with a non-causative diagnosis in a prospective cohort study. Methods: The 227,097 visits to the emergency department were filed by personal identification number and included information on gender, age, admission, discharge, and diagnosis. The visits were classified by main diagnosis at discharge into those with non-causative diagnosis and those with other diagnoses. Mortality per 100,000 within 8, 15 and 30 days and the corresponding hazard ratio (HR) and 95% confidence intervals (CI) were calculated for all causes of death and for selected causes of death in a time-dependent analysis. Results: The HRs of all causes of death for patients with a non-causative diagnosis were 0.64 (95% CI 0.41–1.01) within 8 days, 0.70 (95% CI 0.50–0.99) within 15 days, and 0.82 (95% CI 0.65–1.04) within 30 days as compared to those with a causative diagnosis. The HRs within 30 days among those with a non-causative diagnosis at discharge were 1.48 (95% CI 1.03–2.13) for malignant neoplasm, 3.72 (95% CI 1.44–9.60) for suicide, and 0.50 (95% CI 0.32–0.79) for diseases of the circulatory system. Conclusion: Death within 8 days after discharge home from the ED is a rare event. Death of patients that occur shortly after discharge who had received a non-causative diagnosis as the main diagnosis may indicate a misjudgement of the patients’ condition at that time.