Antenatal magnesium sulphate reduces the risk of cerebral palsy in babies born <30 weeks’ gestation. A guideline for its use in women at imminent risk of preterm birth was implemented at National Women's Health, Auckland City Hospital in 2012. This prospective audit assessed adherence to the guideline in women delivering at <30 weeks in the first year after its implementation. Magnesium sulphate was safely administered to 58 of 71 (82%) eligible women and 58 of 61 (95%) of women where it was clinically appropriate and practically achievable.