To test the hypothesis that the development of tracheal stenosis would depend on the extent of tracheal cartilaginous injury, either 90 degrees (n=6) or 180 degrees (n=6) of anterior wall of 4 tracheal rings were cauterized in 12 mongrel dogs using Nd-YAG laser. Beginning at 3 weeks after cauterization, 180 degrees tracheal injury resulted in life-threatening tracheal stenosis whereas 90 degrees injury did not. Gross and microscopic examinations showed that after 180 degrees injury, tracheal stenosis was accompanied by the loss of tracheal cartilage and dense fibrosis. These results indicate that tracheal stenosis depends on the extent of tracheal injury in experimental canine model.