Twenty-two children or 14% of children on opioid therapy underwent 30 opioid rotations. Mucositis was the cause of pain in 19 (70%) children, bone pain in 3 (11%) children, and postoperative, visceral, or neuropathic pain in the remainder. The opioid was rotated either for excessive side effects with adequate analgesia (70%), excessive side effects with inadequate analgesia (16.7%), or tolerance (6.7%). Five (23%) children required two rotations, 3 during the same admission. The favored rotations were morphine to fentanyl in 20 (67%) children and fentanyl to hydromorphone in 6 (20%). Adverse opioid effects were resolved in 90% of cases, all failures occurred when morphine was rotated to fentanyl.