OBJECTIVE: The HIV Prevention Trials Network (HPTN) 065 trial sought to expand HIV screening of emergency department (ED) patients in Bronx, New York, and Washington, D.C. This study assessed the testing costs associated with different expansion processes and compared them with costs of a hypothetical optimized process. METHODS: Micro-costing studies were conducted in two participating EDs in each city that switched from point-of-care (POC) to rapid-result laboratory testing. In three EDs, laboratory HIV testing was only conducted for patients having blood drawn for clinical reasons; in the other ED, all HIV testing was conducted with laboratory testing. Costs were estimated through direct observation and interviews to document process flows, time estimates, and labor and materials costs. A hypothetical optimized process flow used minimum time estimates for each process step. National wage and fringe rates and local reagent costs were used to determine the average cost (excluding overhead) per completed nonreactive and reactive test in 2013 U.S. dollars. RESULTS: Laboratory HIV testing costs in the EDs ranged from $17.00 to $23.83 per completed nonreactive test, and POC testing costs ranged from $17.64 to $37.60; cost per completed reactive test ranged from $89.29 to $123.17. Costs of hypothetical optimized HIV testing with automated process steps were approximately 45% lower for nonreactive tests and 20% lower for reactive tests. The cost per ED visit to conduct expanded HIV testing in each hospital ranged from $1.21 to $3.96. CONCLUSION: An optimized process could achieve additional cost savings but would require an investment in electronic system interfaces to further automate testing processes.