© 2014 American Academy of Allergy, Asthma & Immunology. Background It remains unclear whether the quality of acute asthma care in US emergency departments (EDs) has improved over time.Objectives We investigated changes in concordance of ED asthma care with 2007 National Institutes of Health guidelines, identified ED characteristics predictive of concordance, and tested whether higher concordance was associated with lower risk of hospitalization.Methods We performed chart reviews in ED patients aged 18 to 54 years with asthma exacerbations in 48 EDs during 2 time periods: 1997-2001 (2 prior studies) and 2011-2012 (new study). Concordance with guideline recommendations was evaluated by using item-by-item quality measures and composite concordance scores at the patient and ED levels; these scores ranged from 0 to 100.Results The analytic cohort comprised 4039 patients (2119 from 1997-2001 vs 1920 from 2011-2012). Over these 16 years, emergency asthma care became more concordant with level A recommendations at both the patient and ED levels (both P <.001). By contrast, concordance with non-level A recommendations (peak expiratory flow measurement and timeliness) decreased at both the patient (median score, 75 [interquartile range, 50-100] to 50 [interquartile range, 33-75], P <.001) and ED (mean score, 67 [SD, 7] to 50 [SD, 16], P <.001) levels. Multivariable analysis demonstrated ED concordance was lower in Southern and Western EDs compared with Midwestern EDs. After adjusting for severity, guideline-concordant care was associated with lower risk of hospitalization (odds ratio, 0.37; 95% CI, 0.26-0.53).Conclusions Between 1997 and 2012, we observed changes in the quality of emergency asthma care that differed by level of guideline recommendation and substantial interhospital and geographic variations. Greater concordance with guideline-recommended management might reduce unnecessary hospitalizations.