The size of the pharyngeal airway can play an important role in predetermining obstructive sleep apnea, a disorder characterized by recurrent pharyngeal airway obstruction during sleep. Thus it is of particular interest for the orthodontist to know which individuals are more likely to have narrow airways and if airway dimensions can be altered by treatment. To study the latter, changes in the pharyngeal airway in growing children and adolescent were evaluated over a period of 12 years and compared with a group of children who received activator-headgear Class II treatment. In another study, the airways on two-dimensional lateral cephalograms were compared with three-dimensional computed airways.