Approximately 6% to 10% of women entering jails are pregnant. Women entering jail are often poor, medically underserved, and at high risk for substance abuse and unplanned pregnancies. We hypothesize that many women who are pregnant when entering jail have had a prior incarceration and conceived soon after release. We reviewed charts of 269 pregnant women entering the Rhode Island jail between August 1997 and November 2002. Of these women, 52.4% had prior incarcerations. In addition, 117 women conceived within 1 year of a prior release (50% within 90 days, 24% within 91 to 180 days, and 26% more than 180 days postrelease). Women who conceived within 90 days were more likely to be incarcerated for more than 30 days while pregnant than women who conceived after 90 days (relative risk 2.38; 95% confidence interval 1.12 to 5.07). Providing contraceptive services at the time of release may help decrease the number of women who enter jail pregnant.