OBJECTIVE To investigate the efficacy and safety of oral transmucosal fentanyl (OTFC) in providing analgesia and sedation for painful diagnostic procedures in children. METHODS Randomized, placebo-controlled clinical trial. METHODS Forty-eight children referred to the University Connecticut Division of Pediatric Hematology/Oncology for bone marrow aspiration or lumbar puncture were randomized to receive either OTFC (15 to 20 micrograms/kg) or a placebo lollipop. Thirty minutes after administration, the procedure was begun. An anesthesiologist monitored the child's heart rate, blood pressure, and oxygen saturation every 10 minutes. At the conclusion of the procedure, the nurse, the child's parent, and all children over 8 years of age were asked to rate the pain associated with the procedure using a 1 to 10 visual analogue scale. Young children (less than 8) used a modified scale, the Oucher, yielding a 0 to 5 score. RESULTS Significant differences in pain ratings between the OTFC and placebo groups were noted on the pain scores of the parents (P = .005), nurses (P = .001), younger children (P = .006), and older children (P = .013), and median pain scores in the OTFC group were reduced to tolerable levels. Vomiting (P = .003) and itching (P = .001) were more common in the OTFC group, but no clinically significant vital sign deviations occurred. CONCLUSIONS OTFC is safe and effective for use in relieving the pain of pediatric procedures, but frequency of vomiting may restrict its clinical usefulness.