Use of electronic alerts in clinical practice has had mixed effects on providers' prescribing practices. Little research has explored the use of electronic alerts for improving screening practices. New York City has one of the highest rates of HIV in the United States. Recent New York State legislation requires healthcare providers to offer an HIV test to patients aged 13-64 years during a clinical encounter. Adhering to this requirement is particularly challenging in emergency department (ED) settings, which are frequently overcrowded and under-resourced. The purpose of this study was to evaluate the effect of an electronic "hard-stop" alert on HIV testing rates in the ED. Approximately four months of data were reviewed before and after the implementation of the alert. We found that use of the electronic alert significantly increased documentation of offering an HIV test (O.R. = 267.27, p<0.001) and resulted in a significant increase in HIV testing. Findings from this study add to the current knowledge about the use of electronic alertsfor improving disease screening.