We used Centers for Disease Control and Prevention HIV Counseling and Testing System data from 2007 to determine the percentage and characteristics of persons newly identified as HIV-positive in US correctional facilities. The newly identified HIV positivity was 0.7%, and 30% of detainees newly identified with HIV were categorized as having low-risk heterosexual contact or no acknowledged risk. Correctional facilities should provide detainees with routine opt-out HIV testing, unless the prevalence of previously undiagnosed HIV infection has been documented to be less than 0.1%.