The objective of this study is to assess the safety of treatment with Duragesic® (a transdermal patch delivering the narcotic pain-reliever fentanyl) in doses of 12.5, 25, 50, 75 and 100 micrograms/hour in pediatric subjects requiring narcotic pain relief therapy. Particular attention is paid to appropriate dose conversion to Duragesic® therapy from the subject's current narcotic pain relief therapy, and to the parameters for increasing the Duragesic® dose to achieve analgesic effectiveness. Pharmacokinetics (fentanyl levels in the bloodstream during treatment) will also be assessed.