Four cases of acute cervical cord injury treated by posterior midline myelotomy are described. The initial neurological examinations of these four patients indicated complete cord lesions. On plain neck X-rays, two exhibited anterior dislocation and two showed no bony injury other than ossification of the posterior longitudinal ligament. Myelography via C1/2 lateral puncture showed complete block of the subarachnoid space in two cases, and incomplete block in the other two. Computed tomographic myelography revealed cord swelling in all cases. Posterior midline myelotomy was performed after administration of a steroid and mannitol, or reduction of spinal dislocation. The time from injury to myelotomy ranged from 5 to 21 hours. No patient developed new deficits postoperatively. During long-term follow-up, which ranged from 10 to 19 months, all patients showed improvement in motor function of the upper extremities. Sensory disturbances also diminished to some degree. However, in one patient, who underwent myelotomy 18 hours after injury and had shown progressive neurological deterioration before surgery, the improvement in motor function was only slight. In this case, earlier myelotomy may have been more beneficial. These results support the indication for myelotomy in cases of acute cervical cord injury with cord swelling. Particularly if performed early, this procedure is effective in preventing secondary neurological damage.