Pregestational type I and type II diabetes confer an unacceptably high perinatal mortality rate, up to tenfold the background population risk. This renders pregestational diabetes among the highest risk medical conditions in obstetrics. Pregestational diabetes represents a particularly high-risk for evolution of preeclampsia (PET), with incidence rates of PET within this group at approximately 20%. The combination of diabetes and preeclampsia places the pregnancy at heightened risk for hypoxia and stillbirth. The aetiology of PET remains unclear, although placental dysfunction, due to disordered early placental development, is central to the disease process. Early placental disease is followed months later by clinical manifestations of PET, which reflect widespread endothelial dysfunction resulting in vasoconstriction, ischaemia and increased vascular permeability. While not all adverse perinatal outcomes in women with pregestational diabetes are attributed to hypertensive disorders, any therapy that offers the potential to reduce the incidence of preeclampsia in this group deserves close attention. Low-dose aspirin has been investigated for the prevention of preeclampsia owing to its negative effect on thromboxane production, and its safety record in pregnancy is well-established. Therefore, consideration should be given to treating all diabetes-affected pregnant women with aspirin from the first trimester until 36 weeks' gestational age.