CONTEXT Homeless persons face numerous barriers to receiving health care and have high rates of illness and disability. Factors associated with health care utilization by homeless persons have not been explored from a national perspective. OBJECTIVE To describe factors associated with use of and perceived barriers to receipt of health care among homeless persons. DESIGN AND SETTING Secondary data analysis of the National Survey of Homeless Assistance Providers and Clients. SUBJECTS A total of 2974 currently homeless persons interviewed through homeless assistance programs throughout the United States in October and November 1996. MAIN OUTCOME MEASURES Self-reported use of ambulatory care services, emergency departments, and inpatient hospital services; inability to receive necessary care; and inability to comply with prescription medication in the prior year. RESULTS Overall, 62.8% of subjects had 1 or more ambulatory care visits during the preceding year, 32.2% visited an emergency department, and 23.3% had been hospitalized. However, 24.6% reported having been unable to receive necessary medical care. Of the 1201 respondents who reported having been prescribed medication, 32.1% reported being unable to comply. After adjustment for age, sex, race/ethnicity, medical illness, mental health problems, substance abuse, and other covariates, having health insurance was associated with greater use of ambulatory care (odds ratio OR, 2.54; 95% confidence interval CI, 1.19-5.42), inpatient hospitalization (OR, 2.60; 95% CI, 1.16-5.81), and lower reporting of barriers to needed care (OR, 0.37; 95% CI, 0.15-0.90) and prescription medication compliance (OR, 0.35; 95% CI, 0.14-0.85). Insurance was not associated with emergency department visits (OR, 0.90; 95% CI, 0.47-1.75). CONCLUSIONS In this nationally representative survey, homeless persons reported high levels of barriers to needed care and used acute hospital-based care at high rates. Insurance was associated with a greater use of ambulatory care and fewer reported barriers. Provision of insurance may improve the substantial morbidity experienced by homeless persons and decrease their reliance on acute hospital-based care.