BACKGROUND While most guidelines recommend the use of insulin in women whose pregnancies are affected by pre-existing diabetes, oral agents have obvious benefits for patient acceptability and adherence. It is necessary, however, to assess the effects of these anti-diabetic agents on maternal and infant health outcomes. Additionally, women with previous gestational diabetes mellitus are increasingly found to be predisposed to impaired glucose tolerance and, despite the potential need for intervention for these women, there has been little evidence about the use of oral anti-diabetic agents by these women pre-conceptionally or during a subsequent pregnancy. OBJECTIVE To investigate the effect of oral anti-diabetic agents in women with pre-existing diabetes mellitus, impaired glucose tolerance or previous gestational diabetes planning a pregnancy or pregnant women with diabetes mellitus on maternal and infant health.The use of oral antidiabetic agents for management of gestational diabetes in a current pregnancy is evaluated in a separate Cochrane review. METHODS We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (March 2010). METHODS We included randomised and quasi-randomised trials. METHODS Two review authors independently assessed trial eligibility for inclusion. RESULTS We identified 13 trials published as 25 papers using the Cochrane Pregnancy and Childbirth group literature search, and an additional ongoing trial. We have not included any trials in the review. One trial is awaiting assessment and we have excluded twelve trials because they evaluated treatment of women with gestational diabetes or women with polycystic ovary syndrome, were not randomised controlled trials or data were not available. CONCLUSIONS Little randomised evidence is available evaluating the use of oral anti-diabetic agents in women with diabetes mellitus, impaired glucose tolerance, previous gestational diabetes mellitus planning a pregnancy or pregnant women with pre-existing diabetes mellitus. Large trials comparing any combination of oral anti-diabetic agent, insulin and dietary and lifestyle advice in these women, reporting on maternal and infant health outcomes, glycaemic control, women's views on the intervention and long-term health outcomes for mother and child, are required to guide clinical practice.