As emergency department utilization continues to increase, health plans must limit their cost exposure, which may be driven by duplicate testing and a lack of medical history at the point of care. Based on previous studies, health information exchanges (HIEs) can potentially provide health plans with the ability to address this need.To assess the effectiveness of a community-based HIE in controlling plan costs arising from emergency department care for a health plan's members. Albert Tzeel.The study design was observational, with an eligible population (N = 1482) of fully insured plan members who sought emergency department care on at least 2 occasions during the study period, from December 2008 through March 2010. Cost and utilization data, obtained from member claims, were matched to a list of persons utilizing the emergency department where HIE querying could have occurred. Eligible members underwent propensity score matching to create a test group (N = 326) in which the HIE database was queried in all emergency department visits, and a control group (N = 325) in which the HIE database was not queried in any emergency department visit.Post-propensity matching analysis showed that the test group achieved an average savings of $29 per emergency department visit compared with the control group. Decreased utilization of imaging procedures and diagnostic tests drove this cost-savings.When clinicians utilize HIE in the care of patients who present to the emergency department, the costs borne by a health plan providing coverage for these patients decrease. Although many factors can play a role in this finding, it is likely that HIEs obviate unnecessary service utilization through provision of historical medical information regarding specific patients at the point of care.