Background: Bronchiolitis is among the most significant health burdens among infants and young children globally. Clinical practice guidelines from around the world, including those of the American Academy of Pediatrics, recommend against routine use of radiography in the evaluation of infants with bronchiolitis. No nationwide longitudinal assessment of radiography utilization for bronchiolitis has been undertaken following publication of US guidelines in 2006. Objective: To determine if the proportion of children undergoing radiography in US Emergency Departments (EDs) for the evaluation of bronchiolitis has changed following the publication of national guidelines. Design, Setting and Participants: This was a repeated cross-sectional study using the National Hospital Ambulatory Care Survey (NHAMCS) database of nationally representative ED visits from 2007-2015. We included all children <2-years with a discharge diagnosis of bronchiolitis. Survey weighting procedures were applied to estimate the US annual frequency of radiography and to perform multivariable logistic regression to identify factors associated with radiography use. Annual Medicare national average allowable fees were applied to population-level estimates to derive direct costs of radiography use. Main Outcome Measure: Proportion of children with bronchiolitis receiving radiography imaging annually. Results: Throughout the 9-year study-period, an estimated 2.9 (95%CI, 2.4-3.4) million children were diagnosed with bronchiolitis. Median age was 8-months (IQR 5-12), 59% were male, 10% required admission, and a majority presented to non-teaching and non-pediatric hospitals (87% and 77%, respectively). Radiography use averaged 46% (95%CI 40%-53%), both overall and among discharged patients. There was no change in the proportion of infants undergoing radiography by year (range 39%-61%, p-trend=0.87), ), as confirmed in multivariable analysis (AOR 0.99, 95%CI 0.91-1.08) after adjustment for patient age, gender, race, insurance provider, pediatric or teaching hospital and triage acuity. Absolute radiography use (108,530 in 2007, 204,278 in 2015; p-trend=0.001) and direct costs attributable to imaging increased annually ($4.1M in 2007, $7.3M in 2015; p-trend=0.001). Overall, estimated direct costs of radiography exceeded $48M (95%CI $41M-$56M) over the study-period, with $44M (95%CI $36M-$52M) among discharged patients alone. Conclusions: Radiography utilization in the US was high and did not decrease during the 9-year period following publication of national bronchiolitis guidelines. Absolute use of radiography increased annually, as did associated direct costs. Findings suggest an important role for quality improvement initiatives to reduce radiography overuse in this population.