Many women in prison are of reproductive age and therefore may be pregnant at some time during their incarceration. To assess the effect of incarceration on pregnancy outcome, 76 pregnant women imprisoned during their gestation were compared to a control group of 117 nonincarcerated women. Various risk factors including substance abuse, sexually transmitted diseases, urinary tract infections, and outcome variables including premature birth, cesarean section, and neonatal birth weight were analyzed. There was a statistically greater number of drug abusing patients in the incarcerated group as expected (P < 0.001). When length of incarceration is excluded, only a greater prevalence of low birth weight (P < 0.04) and premature birth (P = 0.05) in the former group is noted. However, pregnancy outcome, with respect to cesarean section, premature birth, and low birth weight, significantly improved with increasing duration of gestation spent in prison. Therefore, enforced provision of prenatal care and cessation of high risk behavior appears to have a beneficial effect on maternal and fetal outcome.