The transdermal therapeutic system with fentanyl was released in Germany in 1995. Before and after the release several clinical trials were performed in our pain management unit and in other German pain centers, showing good efficacy after initial dose titration with intravenous patient-controlled analgesia or switching from pretreatment with oral morphine or other opioids. A sequential trial showed less use of laxatives with transdermal fentanyl compared to pretreatment with oral morphine. Safety and efficacy of the transdermal system in clinical practice were confirmed in a nationwide survey with 1005 patients, nearly all of them with cancer pain. Most patients had been treated with opioids, though 22% had received no opioids or only as required before initiation of transdermal fentanyl. The mean duration of transdermal treatment was 71 ± 83 days. Pain relief with transdermal therapy was swift and efficient. Adverse events with the possibility of a causal relationship to transdermal therapy were documented for 26% of the patients, most frequently nausea, vomiting, constipation and drowsiness. Severe neurotoxic or respiratory complications were reported only rarely. Problems with transdermal application were reported by 12% of the patients, with patch detachment and dermatologic symptoms on the site of application being most frequent. Most patients showered regularly with the patches and only three patients reported that patches became loose under the shower or in the bathtub. In a recent prospective trial driving ability was tested in patients with continuous non-cancer pain, who had received stable doses of transdermal fentanyl. Data were available from 90 healthy volunteers matched to 30 patients, of whom 9 were excluded from the analysis because they took additional drugs in violation of the protocol. None of the performance measures for the 21 remaining fentanyl patients was significantly inferior to the controls. In conclusion, experience with the transdermal therapeutic system with fentanyl has been gathered in clinical trials, a large nationwide survey and clinical practice since the release in 1995. The conversion table based on a conversion ratio of 100:1 was safe and efficient in trials and clinical practice. Transdermal fentanyl has become a wellknown and frequently used opioid in the treatment of chronic cancer and non-cancer pain in Germany.