The Affordable Care Act of 2010 expanded health insurance coverage to young adults by allowing them to remain as dependents on their parent's private health insurance until they turn 26 years old. While there is evidence that this law has meaningfully affected the insurance status of young adults, we know very little of how this extended coverage has affected the use of medical care. We study the implications of the expansion for the use of an especially expensive form of medical care, inpatient hospital visits, using the Nationwide Inpatient Sample. We find evidence that compared to those who were excluded from the mandate but close in age, treated young adults 23-25 years of age increased their inpatient visits by 3.5 percent after the policy implementation. Both emergency and non-emergency sources of admissions contributed to this surge. Visits for mental illness increased by 5.5 percent. As a result of the reform, the prevalence of uninsurance among hospitalized young adults decreased by 10.8 percent.