A case is reported of a 69-year-old man who sustained a total atelectasis of his right lung while undergoing ilio-tibial bypass surgery. This patient had a history of chronic obstructive pulmonary disease. The plain chest film showed a possible right-sided segmental atelectasis as well as pleural thickening on the same side. Lung function tests showed up a small obstructive syndrome, with mild hypoxaemia (Pao2 60.5 mmHg). The procedure was performed under epidural anaesthesia, carried out with 20 ml of 0.5% bupivacaine and 0.1 mg fentanyl. The upper level of anaesthesia was T4. The patient was sedated with flunitrazepam. He was given oxygen because arterial blood appeared to be somewhat dark. Despite this, the patient became grey, agitated, and had tachypnoea, together with absent breath sounds on the right side. A chest X-ray confirmed the diagnosis of total atelectasis of the right lung. Fiberoptic bronchoscopy was carried out, and a purulent mucous plug was removed. The patient improved and recovered from this episode totally. Blood gases were measured 1 month later; there was no difference with the preoperative values, except for correction of the hypoxaemia (Pao2 76 mmHg). The different factors possibly involved in the pathogenesis of the plug are discussed. It is likely that general anaesthesia would not have avoided this complication.