One of the most common mechanisms of failure of epidural anesthesia is the misplacement of a catheter. We present two cases of transforaminal escape of catheter which occurred accidentally during lumbar epidural anesthesia. Epidural catheter was inserted to a depth of 4.5 cm and 3.5 cm respectively, then 2% lidocaine 25 ml were injected slowly into the catheter. No analgesia was found except anterior knee area, so Iohexol dye was injected through the catheter for X-ray determination. The epidurogram showed the catheter, which passed through the intervertebral foramen, was to lie outside the epidural space in the paravertebral tissue. Because of the random direction and migration of epidural catheter, we suggest an epidural catheter should be inserted 3cm into the epidural space. Epidurogram with a small dose of contrast material is advisable in the cases of unsatisfactory effect of epidural block, or when some adverse reactions are noted after block.