An 85-year-old man with undiagnosed eventration of the left hemidiaphragm had an above-knee amputation under epidural anaesthesia. His post-operative course was stormy with two episodes of cardiovascular collapse. On the third post-operative day, rupture of the left hemidiaphragm was diagnosed, the bowel had herniated into the left hemithorax. It is proposed that the left hemidiaphragm ruptured spontaneously because of muscular weakness secondary to the thoracic segmental blockade associated with lumber epidural anaesthesia.