Background Oral transmucosal fentanyl citrate is indicated for the treatment of breakthrough pain in adults with cancer who are already receiving maintenance opioid therapy for chronic cancer pain. Purpose To evaluate off-label transmucosal fentanyl citrate use for bone fracture alignment in children. Materials and methods In December of 2010 the Pharmacy and Therapeutics Committee approved a protocol for off-label transmucosal fentanyl citrate use for bone fracture alignment in children older than 3 years old. A retrospective, observational study was carried out December 2010 through October 2011. Inclusion criteria were an ASA (American Society of Anaesthesiologists) physical status 1 or 2 and a body ≥12 kg. Dose to be administered depends on the patient's weight: Between 12 and 22 kg: 200 mcg For patients >23 kg: 400 mcg. Dose can be repeated if it is not effective. The sedoanalgesia is evaluated by Wong-Baker faces pain rating scale and numeric pain rating scale before and after the process. Vital signs like glasgow, hart rate, respiratory drive and oxygen saturation are evaluated during the process. Children's parents must be informed and provide informed consent Results 15 childrens were treated with transmucosal fentanyl during a fracture alignment, 11 boys and 4 girls, the average age of those patients were 8, 26 years old (3–13). Before the process 10/15 patients had between 6 and 10 points in numeric pain rating scale, the rest of them had four or less points. The average pain reduction were 5, 1 points (0–8) – this date were not evaluated in four patients. There was no significant changes in any patient vital signs during and after medication. Only 1/15 patient presented an adverse reaction, with vomiting 60 min after transmucosal fentanyl administration. Conclusions Transmucosal fentanyl analgesia for bone fracture alignment in children could be used as an alternative to other pain medications. It is necessary a larger study to establish an effective dose and to observe its safety use.