Jails provide an underutilized public health opportunity for screening for HIV, sexually transmitted infections (STIs), and viral hepatitis, and for such other infectious diseases as tuberculosis. Incarcerated individuals are more likely to be men, poor, persons of color, and at high risk for HIV. The vast majority of jails in the United States do not screen routinely for HIV or STIs, thereby missing an opportunity for HIV and STI diagnosis, treatment, and prevention. Nesting HIV testing within STI testing and treatment in conjunction with testing and treatment for other infectious diseases, as appropriate based on community prevalence, provides a public health opportunity and will enhance HIV prevention. HIV testing and linkage to care, both within corrections and in the community, comprise an important component of the "seek and treat" strategy to further prevent HIV infection. Jail-based screening of infectious diseases, especially for HIV and STIs, in conjunction with treatment and linkage to community care has thus far been a neglected component of HIV prevention among high-risk communities. Copyright © 2010 by Lippincott Williams & Wilkins.