BACKGROUND: Little is known about population-level sexually transmitted disease (STD) testing in emergency departments. We sought to explore STD testing patterns in emergency departments (EDs) in a large, urban metroplex in North Texas, a high prevalence region. METHODS: ED claims data were extracted from the Dallas Fort Worth Hospital Council databank for patients attending 54 EDs in four counties (Dallas, Tarrant, Collin, and Denton) who were tested for an STD during an ED visit between July 2014 and June 2015. We analyzed patterns of testing for three types of STD tests: 1) combined gonorrhea and chlamydia DNA based tests; 2) HIV antibody tests; and 3) syphilis serological tests. RESULTS: EDs administered at least one STD test to 65,702 unique patients over 1 year; most were ethno-racial minorities (73%), female (72%) and had no known insurance (59%). Only 8% of patients received more than one of these tests at that same visit; of those, 90% were co-tested for HIV. The most common diagnosis code associated with STD testing was “genital/urinary symptoms” (31%). The majority of tests took place at the ED of a single county-funded hospital (42%). Only 36% of all patients had visits that were deemed true emergencies. CONCLUSIONS: Most patients tested for syphilis, HIV or chlamydia/gonorrhea in EDs received only one test type at that visit, and most visits were non emergent in nature. Given shared risk factors for multiple STD and high co-infection rates, EDs serving high-risk populations could consider STD co-testing to help reduce transmission of undiagnosed, untreated infections.