Background Asthma is one of the most common medical illnesses occurring in pregnancy and its incidence amongst the obstetric population is increasing. Previous studies have suggested that asthma is not a benign illness in pregnancy, and can contribute towards increased rates of pregnancy complications. Methods We undertook a retrospective audit of 6458 deliveries during 2008 at The Royal Women's Hospital to determine the perinatal outcomes for women with a self-reported diagnosis of asthma. Results We found that 501 (7.8%) deliveries were to women who identified themselves as asthmatics. Of these, 15.6% reported exacerbations of their asthma symptoms during pregnancy, with the remainder reporting improvement or stabilization. There was an increased rate of preterm birth (12.9%) in the asthmatic population, compared to the non-asthmatic population (OR = 1.48, CI [1.12–1.95], P = 0.005). Asthma remained significantly associated with an increased risk of preterm birth after adjusting for maternal smoking status using logistic regression analysis (Adjusted OR 1.41, CI [1.07–1.86], P = 0.01). Women were also at increased risk of developing pre-eclampsia (OR 1.71, CI [1.09–2.67], P = 0.02) but not fetal growth restriction. Women identifying themselves as asthmatics were also more likely to deliver by caesarean section (OR 1.32, CI [1.09–1.6], P = 0.003). Conclusion These findings suggest that maternal asthma may be associated with an increased risk of preterm birth, pre-eclampsia and caesarean delivery.