A 20-year-old man underwent a 9-hour operation in a left lateral position for the removal of an osteoblastoma involving the pedicles of thoracic vertebrae T-11 and T-12 and for fixation with bond grafting. Immediately after the operation, extensive swelling of the left shoulder area was noted. The radial pulse on the left was intact, and there was movement of the fingers of the left hand, which ceased completely by the following morning. A computerized axial tomographic scan showed extensive swelling of the pectoral, deltoid, and other muscles around the shoulder. An emergency decompression procedure was carried out by dividing the pectoral and anterior scalene muscles; prompt return of some motor activity in the left hand followed, and this gradually returned to normal. This case of what may be termed "axillary" compression syndrome suggests that extra care should be taken to use an adequate axillary roll and to avoid lengthy operations in a lateral position, and indicates a method for decompression.