Cowden syndrome is a rare syndrome of chromosome abnormalities presenting with polyposis of digestive tracts, characteristic skin eruption and neuromuscular disorders. A 56-year-old male patient with Cowden syndrome underwent upper abdominal surgery under general anesthesia followed by post-operative epidural analgesia with buprenorphine. Proposed total gastrectomy was not performed because of massive invasion of carcinoma in the abdominal cavity and gastrojejunostomy was done instead. The anesthesia was satisfactory with inhalation of nitrous oxide and enflurane with intravenous vecuronium. Neuromuscular monitoring with electric twitch-responses of the hand showed normal patterns throughout the anesthesia. The recovery from anesthesia and neuromuscular blockade was prompt. Intermittent epidural buprenorphine, twice a day (0.2 mg of buprenorphine in 9 ml of normal saline for one time) was started just after the recovery of anesthesia and continued for four days. Delirium occurred two days after beginning epidural buprenorphine and disappeared three days after its discontinuation. The patient died 52 days after the operation from obstructive jaundice and sepsis. The delirium, therefore, seems to have been caused by buprenorphine possibly due to its impaired metabolism by the liver. Although we did not experience any abnormal neuromuscular reactions to vecuronium or anesthetic agents, it is important to perform preoperative neuromuscular examinations and peri-operative monitoring in the anesthetic management of a patient with this syndrome.