Emergency hospital utilization rates for asthma remain high despite advances in asthma controller medications and the presence of widely accepted asthma treatment guidelines. To explore this phenomenon, we analyzed administrative data to determine characteristics of patients seen in the emergency department (ED) for asthma. Complete pharmacy and diagnostic coding records were obtained from consecutive adults (aged 19-56 years) treated for asthma in the ED of a closed-network health maintenance organization between April and July of 2002. Subjects were stratified into asthma severity categories (persistent or non-persistent) based on the National Committee for Quality Assurance 2006 Health Plan and Employer Data and Information Set (HEDIS) criteria for persistent asthma. Eighty-one unique patients made a total of 89 ED visits for asthma during the study period. Of the 89 total ED visits for asthma, 44 (49%) occurred in patients that did not meet HEDIS criteria for persistent asthma. Of the 81 unique patients making asthma-related ED visits, 41 (51%) did not meet HEDIS criteria for persistent asthma. Over one-half (51%) of this nonpersistent population were not given either asthma reliever or asthma controller medications during the 12-month period before their index ED visit. Over the 24-month period before their index ED visit, 37% of nonpersistent patients were dispensed neither asthma reliever nor controller medications. Patients that do not meet HEDIS criteria for persistent asthma account for a substantial percentage of asthma-related ED visits. These patients have a history of low use of asthma medications before their ED visit.