The authors describe a case of accidental catheterization of the subdural extra-arachnoid space during epidural analgesia for labour. The epidural catheter had been inserted at the L3-L4 interspace without any problem. A severe hypotension occurred 90 min after the onset of analgesia. A T4 upper sensory level was associated with a complete motor blockade. Total spinal anaesthesia was suspected but ruled out because of delayed onset of analgesia. Extensive epidural anaesthesia was also eliminated as the local anaesthetic dose (15 mL of bupivacaine 0.125%) was not excessive for this patient. After delivery, a water-soluble contrast medium (10 mL of Omnipaque 180) was injected through the catheter and subsequent radiograph of spine showed subdural spread of the contrast medium. This complication might occur more frequently than usually thought and may be life-threatening. Anaesthetic management is discussed in the case of Caesarean section during labour.