The combined spinal-epidural technique is widely used in obstetric anaesthetic practice. Epidural catheter migration through a dural hole is a theoretical but rarely described complication. We report a case of acute and life-threatening respiratory depression following administration of diamorphine through an epidural catheter after a single space combined spinal-epidural technique for caesarean section. We believe this complication occurred as a result of catheter migration through a dural hole into the subdural space and rupture of the thin arachnoid layer causing massive subarachnoid blockade.