Study Objectives: Hospitalizations that occur shortly after emergency department (ED) discharge may indicate opportunities to improve ED care. There currently is limited population-level information about such events. In this hypothesis-generating analysis, we identified hospital- and visit-level predictors of 7-day unscheduled hospital admission after ED discharge.Methods: We conducted a retrospective cohort analysis of adult (age>18 years) ED visits resulting in discharge from all non-federal California hospitals in 2007. The primary outcome was unscheduled hospital admission within 7 days of ED discharge. Candidate predictors included hospital structural characteristics, patient demographic information, and ED primary discharge diagnosis. We fit multivariable, hierarchical logistic regression to account for clustering of ED visits by hospitals.Results: The study cohort contained a total of 5,035,833 visits to 288 facilities in 2007. Readmission within 7 days of ED discharge occurred in 130,526 (2.6%). In multivariate analysis, 7-day readmission was associated with having Medi-Cal, California's Medicaid program, (OR 1.4, 95% CI 1.4-1.5) or Medicare insurance (OR 1.5, 95% CI 1.5-1.6), and eloping or leaving against medical advice (OR 1.9, 95% CI 1.9-2.0). The 6 most common ED discharge diagnoses associated with the outcome were renal disease (OR 4.1, 95% CI 3.6-4.6), congestive heart failure (OR 3.2, 95% CI 3.0-3.4), diseases of the blood which include a diagnosis of anemia and sickle cell disease (OR 3.2, 95% CI 3.0-3.4), neoplasms (OR 2.9, 95% CI 2.7-3.1), mental illness (OR 2.6, 95% CI 2.6-2.7), and non-infectious lung disease including pleurisy, pneumothorax, and pneumonitis (OR 2.6, 95% CI 2.4-2.9). Hospital characteristics associated with readmission were for-profit status (OR 1.2, 95% CI 1.1-1.3) and teaching affiliation (OR 1.2, 95% CI 1.0-1.3).Conclusion: We found that 2.6% of patients discharged from California emergency departments were readmitted to a hospital bed within 7 days. We identified several hospital structural features, patient characteristics, and ED discharge diagnoses that are associated with increased risk of early readmissions. Further studies of causal pathways are needed to identify interventions to reduce potentially avoidable readmissions. Study Objectives: Hospitalizations that occur shortly after emergency department (ED) discharge may indicate opportunities to improve ED care. There currently is limited population-level information about such events. In this hypothesis-generating analysis, we identified hospital- and visit-level predictors of 7-day unscheduled hospital admission after ED discharge. Methods: We conducted a retrospective cohort analysis of adult (age>18 years) ED visits resulting in discharge from all non-federal California hospitals in 2007. The primary outcome was unscheduled hospital admission within 7 days of ED discharge. Candidate predictors included hospital structural characteristics, patient demographic information, and ED primary discharge diagnosis. We fit multivariable, hierarchical logistic regression to account for clustering of ED visits by hospitals. Results: The study cohort contained a total of 5,035,833 visits to 288 facilities in 2007. Readmission within 7 days of ED discharge occurred in 130,526 (2.6%). In multivariate analysis, 7-day readmission was associated with having Medi-Cal, California's Medicaid program, (OR 1.4, 95% CI 1.4-1.5) or Medicare insurance (OR 1.5, 95% CI 1.5-1.6), and eloping or leaving against medical advice (OR 1.9, 95% CI 1.9-2.0). The 6 most common ED discharge diagnoses associated with the outcome were renal disease (OR 4.1, 95% CI 3.6-4.6), congestive heart failure (OR 3.2, 95% CI 3.0-3.4), diseases of the blood which include a diagnosis of anemia and sickle cell disease (OR 3.2, 95% CI 3.0-3.4), neoplasms (OR 2.9, 95% CI 2.7-3.1), mental illness (OR 2.6, 95% CI 2.6-2.7), and non-infectious lung disease including pleurisy, pneumothorax, and pneumonitis (OR 2.6, 95% CI 2.4-2.9). Hospital characteristics associated with readmission were for-profit status (OR 1.2, 95% CI 1.1-1.3) and teaching affiliation (OR 1.2, 95% CI 1.0-1.3). Conclusion: We found that 2.6% of patients discharged from California emergency departments were readmitted to a hospital bed within 7 days. We identified several hospital structural features, patient characteristics, and ED discharge diagnoses that are associated with increased risk of early readmissions. Further studies of causal pathways are needed to identify interventions to reduce potentially avoidable readmissions.