Nitrous oxide in modern anesthetic practice is used as a carrier gas for more potent volatile anesthetics during general anesthesia and as an analgesic during labor and childbirth. Nitrous oxide is easily administered to parturients using a facemask or mouthpiece and a tank or wall supply of N2O/O2 mixture. The primary controversies surrounding the use of nitrous oxide in labor analgesia consider efficacy, side effects, and safety. Possible side effects of nitrous oxide range from the unpleasant (nausea) to the potentially catastrophic (uterine atony). Most studies that have examined the efficacy of nitrous oxide in obstetric anesthesia practice have also documented side effects. There are several controversial safety issues surrounding the use of nitrous oxide in the labor and delivery suite. The potential exists for environmental contamination with resultant occupational exposure by healthcare workers and others.