The U.S. Centers for Disease Control and Prevention (CDC) now recommends testing all health care patients for HIV-regardless of their reported risk behaviors-using an "opt-out" approach in which patients are informed that an HIV test will be conducted unless they explicitly decline to be tested. These new testing procedures will facilitate the identification of persons living with HIV who are unaware of their infection. However, some of these newly diagnosed persons may not previously have considered the possibility that they might have HIV and may be ill-equipped to cope with an HIV diagnosis. The present commentary reviews the potential reactions of persons who receive unanticipated HIV-positive diagnoses and suggests that additional research is needed to better understand these reactions and associated harms.