Diabetes mellitus complicates 3-5% of all pregnancies and is a major cause of perinatal morbidity and mortality, as well as maternal morbidity. The availability of a variety of new insulins, the insulin pump, and self-monitoring of blood glucose have revolutionized the care of the pregnancy complicated by diabetes mellitus. However, challenges remain in caring for the pregnant patient with pregestational diabetes. Relatively few women receive preconceptional counseling, and major fetal malformations as a result of poor glucose control before and during the early weeks of gestation have emerged as the major cause of perinatal mortality. When the patient has diabetic vasculopathy, the obstetrician, maternal-fetal specialist, and/or endocrinologist and other members of the health care team must perform a challenging balancing act that promotes fetal health while minimizing maternal risk. As obesity increases in this country and our population becomes more diversified, the rate of gestational diabetes mellitus (GDM) will rise. Although there is controversy regarding which diagnostic standards to use for GDM, there is agreement that excellent blood glucose control, with diet and, when necessary, insulin will result in improved perinatal outcome. Finally, the goal of our educational programs should be not only to improve pregnancy outcome but also to promote healthy lifestyle changes for the mother that will last long after delivery.