We prospectively studied the efficacy and safety of self-administered nitrous oxide analgesia for 54 children undergoing closed reductions of fractures in the emergency department. No child was excluded from entry into the study because of fracture type. Nitrous oxide was the sole source of analgesia. The average Children's Hospital of Eastern Ontario pain score (CHEOPS) rated by the emergency medicine physician observing the reduction was 9.1 (range 6-13). Ninety-one percent of children obtained an analgesic effect; however, 46% of children had a CHEOPS score of > or = 10, indicating significant pain. A statistically significantly higher proportion of failures using nitrous-oxide analgesia occurred in patients with completely displaced radius/ulna fractures (p = 0.027). No complications such as vomiting, respiratory depression, or a change in oxygen saturation resulted from the use of nitrous oxide.