Nonphysician providers (NPPs) increasingly perform imaging-guided procedures, but their roles interpreting imaging have received little attention. We characterize diagnostic imaging services rendered by NPPs (i.e., nurse practitioners and physician assistants) in the Medicare population. Using 1994–2015 Medicare Physician/Supplier Procedure Summary Master Files, we identified all diagnostic imaging services, including those billed by NPPs, and categorized these by modality and body region. Using 2004–2015 Medicare Part B 5% Research Identifiable File Carrier Files, we separately assessed state-level variation in imaging services rendered by NPPs. Total and relative utilization rates were calculated annually. Between 1994 and 2015 nationally, diagnostic imaging services increased from 339,168 to 420,172 per 100,000 Medicare beneficiaries (an increase of 24%). During this same period, diagnostic imaging services rendered by NPPs increased 14,711% (from 36 to 5332 per 100,000 beneficiaries) but still represented only 0.01% and 1.27% of all imaging in 1994 and 2015, respectively. Across all years, radiography and fluoroscopy constituted most of the NPP-billed imaging services and remained constant over time (e.g., 94% of all services billed in 1994 and 2015), representing only 0.01% and 2.1% of all Medicare radiography and fluoroscopy services. However, absolute annual service counts for NPP-billed radiography and fluoroscopy services increased from 10,899 to 1,665,929 services between 1994 and 2015. NPP-billed imaging was most common in South Dakota (7987 services per 100,000 beneficiaries) and Alaska (6842 services per 100,000 beneficiaries) and was least common in Hawaii (231 services per 100,000 beneficiaries) and Pennsylvania (478 services per 100,000 beneficiaries). Despite increasing roles of NPPs in health care across the United States, NPPs still rarely interpret diagnostic imaging studies. When they do, it is overwhelmingly radiography and fluoroscopy. Considerable state-to-state variation exists and may relate to local care patterns and scope-of-practice laws.Valeria Makeeva, C. Matthew Hawkins, Andrew B. Rosenkrantz, Danny R. Hughes, Laura Chaves and Richard Duszak, Jr.