Strong opioids are recommended for treating severe cancer pain in the advanced stages of the disease. Few data are available concerning the efficacy of buprenorphine in cancer pain. We compared transdermal buprenorphine 70 microg/h (BUP TDS) to placebo in an enriched design study. Opioid-tolerant patients with cancer pain requiring strong opioids in the dose range of 90-150 mg/d oral morphine equivalents entered a two-week run-in phase, during which they were converted to BUP TDS. Patients who could be stabilized on BUP TDS were randomized to BUP TDS or placebo patch for a two-week maintenance phase. Rescue medication (buprenorphine sublingual tablets 0.2mg) was allowed as required. Response was defined as a mean pain intensity of <5 (0-10 scale) and a mean daily buprenorphine sublingual tablet intake of < or =2 tablets during the maintenance phase. Of 289 patients who entered the run-in phase, 100 discontinued treatment due to lack of efficacy or adverse events; 189 patients continued treatment in the maintenance phase (94 BUP TDS, 95 placebo), of whom 31 discontinued treatment (7 BUP TDS, 24 placebo). A significant difference in the number of treatment responders was observed: 70 BUP TDS (74.5%, 65.7-83.3) vs. 47 placebo (50%, 39.9-60.1) (P=0.0003). This result was supported by a lower daily pain intensity, lower intake of buprenorphine sublingual tablets and fewer dropouts in the BUP TDS group. The incidence of adverse events was slightly higher for BUP TDS. In conclusion, BUP TDS 70 microg/h is an efficacious and safe treatment for patients with severe cancer pain.