Public health agencies can use jail as an opportunity to reach populations disproportionately affected by sexually transmitted infections (STI). The emphasis that STI control programs place on screening jail entrants varies considerably. Nine million individuals passed through U.S. jails in 2005, many in counties where STIs are rare. A pilot program of screening for Neisseria gonorrhoeae and Chlamydia trachomatis was implemented at the intake sites for the combined jail and prison system of Rhode Island, a state with a low prevalence of STIs. Prevalence of either gonorrhea or chlamydia among detainees was 4.6%, but in women aged 25 and younger, the rate was 24 times that of similar-aged women statewide. Screening led to treatment for 22 (81%) of the infected inmates and 10 of their partners. The heterogeneity of both jail demographics and STI epidemiology suggests a need to tailor the choice of screening strategy to local conditions.