A systematic review was conducted to determine the efficacy and safety of nitrous oxide for labor analgesia. Eleven randomized controlled trials with adequate control groups and outcome assessment by parturients during or shortly after the intervention were used to determine efficacy. To determine adverse outcome, descriptions found in 8 controlled trials and in 8 observational studies were included. A nonsystematic review of studies on occupational exposure was also conducted. Nitrous oxide is not a potent labor analgesic, but it is safe for parturient women, their newborns, and health care workers in attendance during its administration. It appears to provide adequately effective analgesia for many women.