A case is reported of oesophageal perforation which occurred during an attempt to carry out endotracheal intubation. A 54-year-old female patient was scheduled for mastectomy. She had no clinical features likely to predict a difficult endotracheal intubation. After induction with thiopentone, phenoperidine and suxamethonium, three attempts were made to carry out tracheal intubation with a Mallinckrodt Lo-pro tube, internal diameter 7.5 mm. During the third attempt, the oesophagus was accidentally intubated. The diagnosis was made before any insufflation was carried out. Another anaesthetist took over, and intubated the patient. At that time, there was left-sided cervical emphysema which quickly spread. An oesophageal perforation was suspected, and the patient was given 500 mg of metronidazole and 1 g of cefotetan. Postoperatively, the antibiotics were continued, and the patient had nothing by mouth. Oesophagography showed a posterior fistula in the upper third. Conservative treatment was continued until the seventh day, when another oesophagography was carried out. This showed that the perforation had completely healed. This rather rare complication of endotracheal intubation may have a poor prognosis if it results in mediastinitis. The diagnosis and prognosis of this complication and its treatment, whether conservative or surgical, are discussed.