The Affordable Care Act is expected to profoundly affect inpatient hospital utilization, both as a result of expansions in insurance coverage as well as payment and delivery system reforms. The objective of this study is to examine changes in inpatient utilization between 2010 and 2013 in California, following a Medicaid expansion and implementation of the Delivery System Reform Incentive Payment program. Findings show that between 2010 and 2013: (a) the overall number of inpatient admissions increased, mainly because an increase in Medicaid admissions exceeded the decrease in uninsured admissions; (b) the number of preventable admissions did not change; (c) preventable admissions decreased at safety net hospitals that received Delivery System Reform Incentive Payment funds relative to other safety net hospitals. The results suggest that delivery system reforms may help offset the upward pressures on utilization and costs due to coverage expansions.