Objective: This retrospective chart review evaluated the efficacy of oral transmucosal fentanyl citrate (OTFC) in an outpatient cancer pain center for patients experiencing severe exacerbations of pain that exceed usual breakthrough pain levels. Patients: Records were reviewed for all patients who received OTFC at M.D. Anderson's outpatient pain clinic over a three-month time period. OTFC was used in thirty-nine patients experiencing a recent onset of severe pain (greater than or equal to7 on a 0-10 scale). All patients had cancer. cancer-related pain syndromes, and were opioid tolerant with an oral morphine equivalent daily dosage (MEDD) of 40 mg/day. Results: Prior to OTFC treatment, all patients reported a mean pain intensity of 9.0 (SD = 1.2). After OTFC treatment, patients reported a mean intensity of 3.0 (SD = 1.4), a significant reduction in pain intensity (P < 0.001). In most cases, OTFC averted the need for an emergency center visit, parenteral opioids, and hospital admission, which suggests that OTFC may be an effective alternative over intravenous Opioids to rapidly titrate analgesia in selected opioid-tolerant cancer patients experiencing severe pain.