There is increasing interest in the use of cuffed paediatric tracheal tubes, these tubes have a number of advantages and disadvantages. One disadvantage is the decreased margin of safety associated with the use of cuffed tracheal tubes. When using an uncuffed tube, the margin of safety is approximately the length of the trachea, however, for a cuffed tube, this margin is reduced and is the length of the trachea minus the distance between the proximal edge of the cuff and the and the tip of the tube. We have found that, compared with traditional uncuffed tubes, cuffed tubes may be associated with a reduced margin of safety of approximately 50% or more.