Objectives: To determine if differences exist in hospital and intensive care unit (ICU)/operating room admission rates based on health insurance status. Methods: This was a retrospective, cross-sectional study of data from hospital clinical and financial records for all 2001 emergency department (ED) visits (80,209) to an academic urban hospital. Hospital admission and intensive care unit (ICU)/operating room admissions were analyzed, controlling for triage acuity, primary complaint, diagnosis, diagnosis-related group (DRG) severity, and demographics. Multivariate logistic regression models identified factors associated with hospital admission for underinsured (self-pay and Medicaid) compared with other insured (private health maintenance organization, preferred provider organization, worker's compensation, and Medicare) patients. Results: Compared with the other insured group, underinsured patients were less likely, overall, to be admitted to the hospital (odds ratio [OR], 0.82; 95% CI = 0.76 to 0.90), controlling for all other factors studied. Subgroup analysis of common complaints showed underinsured patients with a chief complaint of abdominal pain (OR, 0.67; 95% CI = 0.55 to 0.80) or headache (OR, 0.61; 95% CI = 0.39 to 0.95) had the lowest adjusted ORs for admission to the hospital, compared with other insured patients. Underinsured patients with DRG of “menstrual and other female reproductive system disorders” (OR, 0.17; 95% CI = 0.06 to 0.51) or “esophagitis, gastroenteritis, and miscellaneous digestive disorders” (OR, 0.55; 95% CI = 0.28 to 0.96) also were less likely to be admitted compared with the other insured group. No significant differences in ICU/operating room admission rates were found between insurance groups. Conclusions: Whereas there was no difference in admission rates to the ICU/operating room by insurance status, this single-center study does suggest an association between insurance status and admission to a general hospital service, which may or may not be causally related. Factors other than provider bias may be responsible for this observed difference.