The primary objective of this investigation was to determine if there was a change in emergency medical service (EMS) utilization following implementation of Medicaid expansion under the Affordable Care Act. The National Emergency Medical Service Information System (NEMSIS) data from 2010-2016 were evaluated in an interrupted time series analysis. Data were stratified by pediatric and adult EMS activations. No significant changes in level or trend were observed in adult EMS activations. A significant level change was observed in the pediatric EMS activations; however, the trend change reduced the impact of the level change over the study period. These results suggest that Medicaid expansion was not associated with a significant change in adult EMS use. Further investigation into pediatric EMS activations following Medicaid expansion is indicated, as these results suggest there may have been a temporary effect.