Fentanyl buccal tablet (FBT) is a new opioid formulation providing rapid-onset analgesia for the treatment of breakthrough pain (BTP). This study evaluated FBT for BTP in opioid-tolerant patients with chronic cancer pain. The study had a randomized, double-blind, placebo-controlled design and was conducted at 30 outpatient treatment centers in the United States. Following open-label titration, patients were randomly assigned to 1 of 18 double-blind dose sequences (7 FBT tablets, 3 placebo) to treat 10 BTP episodes. Pain intensity was measured on an 11-point scale (0 = no pain; 10 = worst pain). The primary efficacy measure was the sum of pain intensity differences (PIDs) for the first 60 minutes (SPID60); secondary efficacy measures included PIDs and pain relief (PR) measured from 5 minutes through 2 hours. Adverse events (AEs) were recorded. Of 129 patients enrolled, 87 entered the double-blind phase. SPID60 significantly favored FBT versus placebo (mean +/- SE, 9.7 +/- 0.63 vs 4.9 +/- 0.50; P < 0.0001). Secondary measures also favored FBT: PIDs and PR showed significant differences versus placebo at 10 minutes (0.9 vs 0.5; 0.815 vs 0.606, respectively, P < 0.0001) and all subsequent time points (P < 0.0001). AEs were typical of opioids (eg, nausea, dizziness, fatigue). In conclusion, in this study of opioid-tolerant patients with chronic cancer pain and BTP, FBT was efficacious, well tolerated, demonstrated rapid onset of analgesia (within 10 minutes), and had a sustained effect.