AIM: To investigate the effect of aspirin on obstetric outcomes in women with pre-gestational diabetes mellitus (PGDM). METHOD: Retrospective audit of pregnant women with PGDM from two centres in South-Western Sydney was conducted. Women were categorised into the aspirin group (prescribed aspirin before 16 weeks, gestation) and non-aspirin group (not prescribed aspirin or prescribed aspirin at or after 16 weeks, gestation). The outcomes examined were pre-eclampsia, pre-term delivery and birthweight percentile. RESULTS: Of 494 women, 52 (10.5%) were in the aspirin group. Pre-eclampsia developed in 57 (12.0%) women. There was no association between aspirin use and pre-eclampsia (8 (15.4%) vs 49 (11.1%), CONCLUSION: There was no difference in the rates of pre-eclampsia, pre-term delivery, or birthweight percentile between women with PGDM in aspirin group compared to women in non-aspirin group.