BACKGROUND AND OBJECTIVES:Croup is a clinical diagnosis, and the available evidence suggests that, except in rare cases, ancillary testing, such as radiologic imaging, is not helpful. Given the paucity of inpatient-specific evidence for croup care, we hypothesized that there would be marked variability in the use of not routinely indicated resources (NRIRs). Our primary study objective was to describe the variation and predictors of variation in the use of NRIRs.