There have been cases reported of pneumocephalus, spinal cord and nerve root compression associated with the use of air in the loss of resistance technique during epidural block. However, the manual loss of resistance technique is still widely used by anesthesiologists for identifying the epidural space. A 65-yr-old female requested epidural steroid injection for her low leg radiating pain. A 22-guage Tuohy needle was placed in the L3-4 interspace with the loss of resistance technique using 4 ml air. Aspiration yielded no cerebrospinal fluid. After injection of 1% lidocaine 5 ml as a test dose, 0.25% lidocaine 10 ml with 40 mg triamcinole was infused and she did not show any abnormal signs. After changing to sitting position, however, the patient complained of increasing headache and nausea. After vomiting, she was obtunded. CT scan showed brainstem compression by the air. The patient lost conscioussness for 20 minutes. Four hours later, her neurologic examination was normal except for the headache. She was discharged on the third day after the accident and the headache subsided by the fifth day. As far as we know, this is the first case reported of a brain stem compression by air after epidural technique that induced serious neurologic symptoms.