Angiotensin converting enzyme (ACE) inhibitors are excellent antihypertensive agents and are becoming widely used as first-line therapy for chronic hypertension in women of reproductive age owing to their efficacy and few side effects. Reports of adverse fetal and neonatal effects from the use of ACE inhibitors in pregnancy in both animal and human studies prompted recommendations against their use in human pregnancy by several authors. This review discusses the mechanism of action of ACE inhibitors and the use of ACE inhibitors in pregnancy both in experimental animals and use in human pregnancy. ACE inhibitors used during pregnancy may have untoward effects on the fetus. Based on reports in the literature, one should avoid starting ACE inhibitors during pregnancy and discontinue them in current users if at all possible.