PURPOSE: To assess the effect of insurance status on the probability of admission and subsequent health status of patients presenting to emergency departments. SUBJECTS AND METHODS: We performed a prospective cohort study of patients with common medical problems at five urban, academic hospital emergency departments in Boston and Cambridge, Massachusetts. The outcome measure for the study was admission to the hospital from the emergency department and functional health status at baseline and follow-up. RESULTS: During a 1-month period, 2,562 patients younger than 65 years of age presented with either abdominal pain (52%), chest pain (19%) or shortness of breath (29%). Of the 1,368 patients eligible for questionnaire, 1,162 (85%) completed baseline questionnaires, and of these, 964 (83%) completed telephone follow-up interviews 10 days later. Fifteen percent of patients were uninsured and 34% were admitted to the hospital from the emergency department. Uninsured patients were significantly less likely than insured patients to be admitted, both when adjusting for urgency, chief complaint, age, gender and hospital (odds ratio = 0.5, 95% confidence interval 0.3 to 0.7), and when additionally adjusting for comorbid conditions, lack of a regular physician, income, employment status, education and race (odds ratio = 0.4, 95% confidence interval 0.2 to 0.8). However, there were no differences in adjusted functional health status between admitted and nonadmitted patients by insurance status, either at baseline or at 10-day follow-up. CONCLUSIONS: Uninsured patients with one of three common chief complaints appear to be less frequently admitted to the hospital than are insured patients, although health status does not appear to be affected. Whether these results reflect underutilization among uninsured patients or overutilization among insured patients remains to be determined.