To assess the teratogenic potential of angiotensin-converting enzyme (ACE) inhibitors, we report on 20 prospective pregnancies and 85 identified from articles in the literature. The anomaly rate was 20.6% in small series <10 entrants (95% CI 8.7-37.9%) and 1.4% in larger series > or =10 entrants (95% CI 0.03-7.3%) p=0.0016. The most consistent anomaly seen, skull hypoplasia, along with renal dysfunction appear to be more related to prolonged or late pregnancy exposure than to first trimester exposure. There is little supportive evidence that ACE inhibitors (captopril or enalapril) are teratogenic. There seems to be no absolute reason to discontinue these 2 medications prior to pregnancy, nor to create anxiety when a patient is identified with the combination of early pregnancy and treatment with these medications. There appears to be reason to discontinue the medication in pregnancy but the adverse event rate cannot be assessed because of inadequate prospective information.