Using the Urban Institute's Health Insurance Policy Simulation Model (HIPSM), the authors estimate how the Patient Protection and Affordable Care Act would affect health insurance coverage and spending on acute care for the nonelderly. They find that, for example, under the ACA, the number of nonelderly adults without health insurance would decline by 27.8 million, the cost of uncompensated care provided to the uninsured would drop by 61 percent, the Medicaid expansion would enroll 16.8 million more people, and 43.8 million would be covered through health insurance exchanges (both nongroup and SHOP).