Emergency department (ED) chief-complaint (CC) data increasingly are important for clinical-care and secondary uses such as syndromic surveillance. There is no widely used ED CC vocabulary, but experts have suggested evaluation of existing health-care vocabularies for ED CC.To evaluate the ED CC coverage in existing biomedical vocabularies from the Unified Medical Language System (UMLS).The study sample included all CC entries for all visits to three EDs over one year. The authors used a special-purpose text processor to clean CC entries, which then were mapped to UMLS concepts. The UMLS match rates then were calculated and analyzed for matching concepts and nonmatching entries.A total of 203,509 ED visits was included. After cleaning with the text processor, 82% of the CCs matched a UMLS concept. The authors identified 5,617 unique UMLS concepts in the ED CC data, but many were used for only one or two visits. One thousand one hundred thirty-six CC concepts were used more than ten times and covered 99% of all the ED visits. The largest biomedical vocabulary in the UMLS is the Systematized Nomenclature of Medicine Clinical Terms (SNOMED CT), which included concepts for 79% of all ED CC entries. However, some common CCs were not found in SNOMED CT.The authors found that ED CC concepts are well covered by the UMLS and that the best source of vocabulary coverage is from SNOMED CT. There are some gaps in UMLS and SNOMED CT coverage of ED CCs. Future work on vocabulary control for ED CCs should build upon existing vocabularies.