We experienced three cases of accidental subdural catheterization during epidural combined with general anesthesia. In each case, epidural catheterization was performed before induction of general anesthesia. Aspiration through the catheter and a response to a test dose were negative. Then anesthesia was induced with thiamylal IV and the trachea was intubated with vecuronium IV. Hypotension, which was not easily treated by vasopressors and volume load, occurred after administration of 3 to 8 ml mepivacaine with 1: 200,000 epinephrine through the catheter. We examined position of the catheter by injecting iohexol 240 and confirmed subdural catheterization after surgery. It is often difficult to identify subdural placement of an epidural catheter under general anesthesia since signs of massive sensory blockade are masked by general anesthesia. In each case, we suspected malpositioning of the catheter by severe hypotension due to sympatholysis which was difficult to treat. Subdural catheterization is a complication of epidural anesthesia that probably occurs more frequently than previously recognized and is usually unpredictable during general anesthesia.