The purpose of the present clinical investigation was to determine the risks associated with mild chronic hypertension in pregnancy. Two hundred eleven consecutive pregnancies complicated by mild chronic hypertension (diastolic blood pressure, 90 to 110 mmHg) were analyzed. All patients were followed closely throughout pregnancy with frequent prenatal visits and serial assessment of fetal status. Antihypertensive drugs were discontinued at the time of the first prenatal visit. Only 13% of these patients required antihypertensive medications later in pregnancy. There were 2 stillbirths and 4 neonatal deaths for an overall perinatal mortality of 28.1/1000. However, the majority of deaths (5 of 6) occurred among the 21 patients with superimposed preeclampsia. This subgroup was also characterized by a high rate of growth-retarded infants (32%). For patients without superimposed preeclampsia, 5.3% of the infants were small for gestational age and there was only one perinatal death. Thus, for patients with mild chronic hypertension, discontinuance of antihypertension medications does not adversely affect the antepartum course or perinatal outcome. In fact, in the absence of superimposed preeclampsia, the perinatal mortality for these patients approaches that of the general obstetric population. Therefore, in pregnancies complicated by mild chronic hypertension, factors other than increased blood pressure per se might be responsible for the poor perinatal outcome reported in such pregnancies.