We prospectively studied the efficacy and safety of self-administered nitrous oxide combined with a hematoma block in 100 children who had a closed reduction of a fracture in the emergency department. No child was excluded from the study because of the type of fracture. The average Children's Hospital of Eastern Ontario pain score (CHEOPS), as determined by the emergency-medicine physician who observed the reduction, was 6.8 points (range, 4 to 12 points). The average grade for pain, as recalled by the patient and indicated on a visual-analogue pain scale that ranged from 0 to 10 points, was 6.5 points before the patient received any analgesia and 1.2 points immediately after reduction of the fracture and application of a cast. Ninety-seven patients obtained an analgesic effect from the combination of nitrous oxide and a hematoma block. The three remaining children obtained no effect, and the fracture was reduced with use of general anesthesia. Three additional reductions were technically unsuccessful because of rotational or angular malalignment, and a second reduction was performed with general anesthesia. There were no complications such as vomiting, respiratory depression, a change in the oxygen-saturation level, infection, or nerve injury. We concluded that self-administration of nitrous oxide combined with use of a hematoma block is a safe and effective technique of analgesia for the outpatient reduction of fractures in children.