In the 1980s, David Barker and Colleagues proposed that the major causes of cardiovascular and metabolic diseases have their roots in early development. There is now robust evidence that an hyperglycemic intrauterine environment is responsible not only for significant short-term morbidity in the fetus and the neonate but also for an increased risk of developing diabetes as well as other chronic, noncommunicable diseases at adulthood. The risk is higher in pregestational diabetes, but unrecognized and/or poorly managed gestational diabetes (GDM) may have similar consequences. Although a relatively clear picture of the pathogenesis of the fetal and neonatal complications of maternal diabetes and of their interrelationship is available today, the intimate molecular mechanisms involved in the long term are far from being understood. While the rate of GDM is sharply increasing in association with the pandemic of obesity and of type 2 diabetes over the world, we review here the current understanding of short- and long-term outcomes of fetuses exposed to a diabetic environment.