OBJECTIVE : The aim of this study was to assess national and state-specific changes in emergency department (ED) chest imaging utilization from 1994 to 2015. METHODS : Using aggregate 100% Medicare Physician/Supplier Procedure Summary Master Files for 1994 to 2015, the annual frequency of chest imaging in Medicare Part B beneficiaries in the ED setting was identified, and utilization was normalized to annual Medicare enrollment as well as annual ED visits. Using individual Medicare beneficiary 5% research-identifiable files, similar determinations were performed for each state. RESULTS : Between 1994 and 2015, per 1,000 beneficiaries, ED utilization of chest radiography and CT increased by 173% (compound annual growth rate [CAGR] 4.9%) and 5,941.8% (CAGR 21.6%). Per 1,000 ED visits, utilization increased by 81% (CAGR 2.9%) and 3,915.4% (CAGR 19.2%), respectively. Across states, utilization was highly variable, with 2015 radiography utilization per 1,000 ED visits ranging from 82 (Wyoming) to 731 (Hawaii) and CT utilization ranging from 18 (Wyoming) to 76 (Hawaii). Between 2004 and 2015, most states demonstrated increases in the utilization of both radiography (maximal increase of CAGR 11.0% in Vermont) and CT (maximal increase of CAGR 21.0% in Maine). Nonetheless, utilization of radiography declined in four states and utilization of CT in a single state. CONCLUSIONS : Over the past two decades, ED utilization of chest imaging has increased. This was related not only to an increasing frequency of ED visits but also to increasing utilization per ED visit. Across states, utilization is highly variable, but with radiography and CT both increasing, the use of CT seems additive to, rather than replacing, radiography.