Pain control for paediatric patients undergoing tonsillectomy remains problematic. Tramadol is reported to be an effective analgesic and to have a side-effect profile similar to morphine, but is currently not licensed for paediatric use in the UK. We conducted a prospective, double-blind, randomized controlled trial in children who were scheduled for elective tonsillectomy or adenotonsillectomy at the Royal Aberdeen Children Hospital. Following local ethics committee approval and after obtaining a drug exemption certificate from the Medicines Licensing Agency for an unlicensed drug, we recruited 20 patients each into morphine (0.1 mg.kg(-1)), tramadol (1 mg.kg(-1)) and tramadol (2 mg.kg(-1)) groups. These drugs were given as a single injection following induction of anaesthesia. In addition, all patients received diclofenac (1 mg.kg(-1)) rectally. The postoperative pain scores, analgesic requirements, sedation scores, signs of respiratory depression and nausea and vomiting, as well as antiemetic requirements, were noted at 4-h intervals until discharge. There were no statistically significant differences in age, weight, type of operation or induction of anaesthesia, 4-h sedation and pain scores and further analgesic requirements. There were no episodes of respiratory depression. Morphine was associated with a significantly higher incidence of vomiting following discharge to the wards (75% versus 40%, P=0.03) compared with both tramadol groups. Tramadol has similar analgesic properties, when compared with morphine. The various pharmaceutical presentations and the availability as a noncontrolled substance may make it a useful addition to paediatric anaesthesia if it becomes licensed for paediatric anaesthesia in the UK.