Magnesium sulfate is commonly used in obstetrical practice both as seizure prophylaxis in women with preeclampsia, as well as to inhibit preterm labor contractions. However, despite (and perhaps because of) years of use and provider familiarity, the administration of magnesium sulfate occasionally results in accidental overdose and patient harm. Fortunately, in most instances when potentially fatal amounts of magnesium sulfate are given, the error is recognized before permanent adverse outcomes occur. Nevertheless, a significant and sometimes unappreciated risk of harm to mothers and babies continues to exist. Intravenous magnesium sulfate treatment has become routine practice in obstetrics, but this does not lessen the vigilance required for safe care for mothers and babies. Implementation of the recommendations provided in this article will promote patient safety and decrease the likelihood of an accidental overdose, as well as increase the chances of identifying an error before a significant adverse outcome occurs.