STUDY OBJECTIVE We assess the feasibility, effectiveness, and cost of routinely recommended HIV/sexually transmitted disease screening in an urban emergency department (ED). METHODS From April 2003 to August 2004, patients aged 15 to 54 years were offered rapid HIV testing, and those aged 15 to 25 years were also offered gonorrhea and chlamydia testing (nucleic acid amplification), Monday through Friday, 11 am to 8 pm. Infected patients were referred for treatment and care. Prevalence, treatment rates, and cost were assessed. RESULTS Among 3,030 patients offered HIV testing, 1,447 (47.8%) accepted, 8 (0.6%) tested positive, and 3 (37.5%) were linked to care. Among 791 patients offered sexually transmitted disease testing, 386 (48.8%) accepted, 320 provided urine (82.9%), 48 (15.0%) tested positive, and 42 (87.5%) were treated for gonorrhea or chlamydia. The program cost was $72,928. Costs per HIV-infected patient identified and linked to care were, respectively, $9,116 and $24,309; cost per sexually transmitted disease-infected patient treated was $1,736. The program cost for HIV/sexually transmitted disease screening was only $14,340 more than if we screened only for HIV. CONCLUSION Through ED-based HIV/sexually transmitted disease screening, we identified and treated many sexually transmitted disease-infected patients but identified few HIV-infected patients and linked even fewer to care. However, sexually transmitted disease screening can be added to HIV screening at a reasonable cost.