The importance of the intrauterine and neonatal metabolic environment as possible teratogenic determinants of predispositions to diabetes, obesity and cardiovascular diseases is discussed. Epidemiological, clinical and experimental results suggest that gestational diabetes or even slightly impaired glucose tolerance during pregnancy are important risk factors for the development of an increased Type II- and even Type I diabetes susceptibility in the offspring. In addition, early prenatal undernutrition might also predispose to enhanced risk of Type II diabetes, whereas perinatal overnutrition seems to enhance predominantly Type I diabetes susceptibility. In this context, fetal and/or neonatal hyperinsulinism occurring during a critical period of brain development and leading to permanent malorganization of hypothalamic regulation centres for metabolism and hence to malprogramming of the hypothalamo-pancreatic system, is discussed as a possible reason for lifelong enhanced diabetes susceptibility. In view of epidemiological and experimental findings, an epigenetic maternofetal transmission of such acquired persistent modifications can run over several generations, mediated by gestational hyperglycaemia and fetal or neonatal hyperinsulinism. In conclusion, a partial prophylaxis of diabetes mellitus, obesity and cardiovascular diseases appears to be possible by prevention of gestational diabetes--even mild forms of impaired glucose tolerance during pregnancy--as well as early prenatal undernutrition and perinatal overnutrition.