The Centers for Disease Control and Prevention (CDC) estimates that about one quarter of the 1-1.2 million persons living with HIV/AIDS in the United States are unaware they are infected. Persons who do not know they are HIV infected are unable to access effective treatment and, compared with those who know they are infected with HIV, are more likely to transmit HIV to others. Pregnant women need to know if they are HIV infected so they can take steps to avoid transmitting HIV to their infants and access medical care for themselves. Despite past CDC recommendations for routine, voluntary HIV testing of all persons in acute-care hospitals with high HIV prevalence and those with risks for HIV, many HIV-infected persons who encounter the health-care system are not tested. Promoting HIV testing as a routine part of medical care is a key strategy of the CDC's Advancing HIV Prevention initiative launched in 2003. The CDC has recently revised recommendations for HIV testing of adults, adolescents, and pregnant women in health-care settings to help increase the number of HIV-infected Americans who are aware they are infected so they can receive prevention, care, and treatment. The new recommendations advocate voluntary "opt-out" HIV screening in health-care settings, with appropriate follow-up care and treatment; eliminating requirements for separate, written consent for HIV testing; annual retesting for persons with known risk factors; and expanded rescreening in the third trimester for women who test negative for HIV early in pregnancy. The CDC issued the revised recommendations on September 22, 2006, and is now engaged with numerous professional organizations on practical strategies for implementation.