This multi-centre, observational study examines the efficacy of the therapeutic transdermal fentanyl system (TTS-fentanyl) in children requiring opioids for pain in life-threatening disease. Forty-one children receiving oral morphine (median 60 mg/day) transferred to transdermal fentanyl (median 25 µg/hr) in line with the manufacturer’s dose conversion guidelines. Twenty-six children completed the 15-day treatment phase, seven died due to disease progression and eight were withdrawn because of adverse events, inadequate analgesia or change to parenteral opioids. At 15 days, median fentanyl dose was 75 µg/hr (range 25-250 µg/hr). No serious adverse events were attributed to fentanyl. There was a trend toward improved side effects and convenience with fentanyl. Twenty-three of 26 parents (three missing) and 25 of 26 investigators considered transdermal fentanyl to be better than previous treatment. For all records available (at 15 days or on withdrawal if earlier), 75% (27/36) reported that fentanyl treatment was "good" or "very good". The findings suggest that transdermal fentanyl is both effective and acceptable to children and families.