Purpose:To describe an atypical presentation of intraoperative anaphylaxis due to fentanyl. Clinical features:A 40-yr-old otherwise healthy woman was admitted for abdominal hysterectomy. She denied any drug allergies or past adverse anesthetic reactions. Physical examination, vital signs, and laboratory findings were all within normal limits. Twenty minutes after induction of general anesthesia with propofol, lidocaine, fentanyl, and rocuronium, she developed sudden onset of hypotension and bronchospasm. She was treated with fluids and epinephrine, but nonetheless required mechanical ventilation for 48 hr. Chest x-ray revealed pulmonary edema which resolved over two days. She recovered completely and was discharged home. Subsequent skin testing showed reactions to fentanyl and succinylcholine. Because the patient had not received succinylcholine, the cause of her anaphylaxis was attributed to fentanyl. The patient later returned for her hysterectomy and tolerated spinal anesthesia with bupivacaine and morphine.