Postdate pregnancy is estimated to occur in 3% to 12% of all gestations. Morbidity and mortality rates associated with this common obstetric problem are higher than those with term gestation. The incidence of fetal distress, birth injury, meconium aspiration, congenital malformations, macrosomia, and oligohydramnios is also greater in postdate pregnancy. We prospectively evaluated breast self-stimulation to determine its effect on the incidence of postdate pregnancy. Two hundred low-risk patients at 39 weeks' gestation were randomly assigned to either a control group or a breast-stimulation group. Results showed that breast stimulation reduced the number of pregnancies managed as postdates from 17 per 100 (17%) to five per 100 (5%) (p less than 0.01), a 70% reduction. It is concluded that breast stimulation in postdates pregnancies can decrease significantly the number of patients that must be monitored by biochemical or biophysical means.