BACKGROUND: Patients with intensive care unit (ICU) transfers from hospital wards have higher mortality than those directly admitted from the emergency department. OBJECTIVE: To describe the association between the timing of unplanned ICU transfers and hospital outcomes. DESIGN, SETTING, PATIENTS: Evaluation of 6369 early (within 24 hours of hospital admission) unplanned ICU transfer cases and matched directly admitted ICU controls from an integrated healthcare system. Cohorts were matched by predicted mortality, age, gender, diagnosis, and admission characteristics. Hospital mortality of cases and controls were compared based on elapsed time and diagnosis. RESULTS: More than 5% of patients admitted through the emergency department experienced an unplanned ICU transfer; the incidence and rates of transfers were highest within the first 24 hours of hospitalization. Multivariable matching produced 5839 (92%) case-control pairs. Median length of stay was higher among cases (5.0 days) than controls (4.1 days, P < 0.01); mortality was also higher among cases (11.6%) than controls (8.5%, P < 0.01). Patients with early unplanned transfers were at an increased risk of death (odds ratio, 1.44; 95% confidence interval, 1.26-1.64; P < 0.01); an increased risk of death was observed even among patients transferred within 8 hours of hospitalization. Hospital mortality differed based on admitting diagnosis categories. While it was higher among cases admitted for respiratory infections and gastrointestinal bleeding, it was not different for those with acute myocardial infarction, sepsis, and stroke. CONCLUSIONS: Early unplanned ICU transfers-even within 8 hours of hospitalization-are associated with increased mortality; outcomes vary by elapsed time to transfer and admitting diagnosis. Journal of Hospital Medicine 2011;. (c) 2011 Society of Hospital Medicine.