ABSTRACT: Pregnancy-induced hypertension (PIH) in general and preeclampsia in particular are major causes of maternal and perinatal morbidity. Data from our studies and from a number of prospective controlled trials have suggested that aspirin in doses of 60–150 md/day during the second and third trimester reduces the risk of PIH and improves maternal and neonatal outcomes. The number of patients enrolled in these studies is relatively small. However, metaanalysis of existing trials suggests that low dose aspirin reduces the risk of PIH and severe low birth weight. Although no maternal or neonatal adverse effects associated with aspirin were observed, the use of aspirin in the third trimester has been reported to cause hemostatic abnormalities in both mother and neonate. Other complications associated with prostaglandin synthetase inhibitors include premature closure of the ductus and neonatal primary pulmonary hypertension. The use of aspirin in the first trimester is not associated with increased risk of structural malformations. On the basis of these findings and pending the results of ongoing large-scale randomized multicenter trials, we suggest that daily low dose aspirin (1 to 2 mg/kg/day) be recommended only for select women at high risk for developing PIH and its associated complications.