Summary We report a catastrophic postoperative complication of a prolonged interscalene block performed under general anaesthesia. The course of the anaesthetic was uneventful and the patient remained stable during his stay in the recovery area with the operative extremity paralysed and insensate. No further local anaesthetic was administered until later that day when the patient received 10 ml bupivacaine 0.25% through the catheter. Upon completion of the top‐up dose, no change in the patient’s status was noticed. The patient was next assessed 6.5 h later when he was found dead in his bed. A postmortem CT scan revealed the catheter to be sited intrathecally, presumably the result of dural sleeve penetration.