RESUMEN
Undocumented immigrants were excluded from the health benefit Marketplaces created by the Affordable Care Act partly because of claims that they contribute to problems such as high costs and emergency department (ED) crowding. This article examines the likely health care use and costs of undocumented immigrants in California in 2009-10. Using data from the 2009 California Health Interview Survey (CHIS), we developed a model that estimated the state's adult and child undocumented immigrant population, since the survey does not explicitly inquire about undocumented status. The survey also provided information on insurance status, doctor visits, and ED visits in the previous year. We found that undocumented immigrants in California, and the uninsured among them, had fewer or similar numbers of doctor visits, ED visits, and preventive services use compared to US citizens and other immigrant groups. Allowing undocumented immigrants to purchase insurance in the Marketplaces and ensuring receipt of low-cost preventive services can contribute to lower premiums and reduce resource strains on safety-net providers.