Objectives The Centers for Disease Control and Prevention recommends routine opt-out HIV screening in health care settings. Our goal was to evaluate the feasibility and yield of this strategy in the emergency department (ED) and to compare it to the expected yield of physician-directed testing. Methods This is a cross-sectional study in an urban ED during random shifts over 1 year. Patients were ineligible for screening if they were younger than 18 years or older than 64, a prisoner, a victim of sexual assault, in an ED resuscitation room, or had altered mental status. Research associates administered rapid HIV tests and conducted standardized interviews. The patients' ED physician, blinded to the HIV result, was asked if they would have ordered a rapid HIV test if it had been available. Results Of 7756 ED patients, 3957 (51%) were eligible for HIV screening, and 2811 (71%) of those did not opt out. Routine testing yielded 9 new HIV cases (0.32% of those tested; 95% confidence interval, 0.16%-0.63%). Physician-directed testing would have missed most of these infections: 2 of the 785 patients identified by physicians for testing would have been newly diagnosed with HIV (0.25%; 95% confidence interval, 0.04%-1.0%). Of the 9 new HIV cases, 5 established HIV care, and their median CD4 count was 201 cells/μL (range, 71-429 cells/μL). Conclusions Routine opt-out HIV screening was feasible and accepted by a majority of ED patients. The yield of this strategy only modestly exceeded what may have been observed with physician-directed testing.