Nitrous oxide is a gas that has been used to provide analgesia to patients for more than a century. Its modern use started in the late sixties when a mixture of 50% nitrous oxide/50% oxygen was prepared. Nitrous oxide/oxygen provides analgesia within 3 minutes of inhalation and this analgesic effect disappears in less than 4 minutes after cessation. Its administration is very easy and a complete or partial pain relief is observed in 75 to 81% of patients. The gas mixture has been found to be safe with few side effects and no significant adverse reactions. Diffusion hypoxia which could lead to hypoxemia was reported in 1955, but recent work does not confirm this complication. Nitrous oxide/oxygen mixture constitutes an excellent drug to control procedure-related pain in children. This articles describes the history, the pharmacology, and the clinical uses of nitrous oxide/oxygen in children.