Pregestational diabetes mellitus (DM) is associated with adverse fetal and maternal outcomes. Studies suggest that optimal control of diabetes before and during pregnancy minimises these risks. There are few recent reviews of outcomes of pregnancies complicated by DM in Australia. Ninety-three pregnancies in women with DM at our hospital since 1989 were identified. We collected data for maternal age, type of diabetes, duration of therapy, complications of diabetes, maternal complications of pregnancy and fetal outcomes including malformations. The rate of pregnancy planning with optimal glycaemic control at conception was low in our population, particularly in patients with Type 1 diabetes. Women who smoked had worse glycaemic control, and a higher rate of miscarriage. There was a high rate of Caesarean section, particularly in those women with Type 1 diabetes (77.4%). The rate of Caesarean section was lower in planned pregnancies. There were no perinatal deaths. The number of neonates with major congenital anomalies was high (13%) in the Type 1 population. It is important to increase the rates of prepregnancy planning and to optimise glycaemic control before pregnancy. In many cases there has been a long interval between diagnosis and pregnancy, so all women with diabetes should receive counselling at frequent intervals about pregnancy and the importance of planning. Women who planned their pregnancies had improved outcomes, with decreased rate of Caesarean section, better glycaemic control and better neonatal Apgar scores. Women with diabetes should not smoke during pregnancy because of the increased risk of miscarriage and poorer glycaemic control.