Radiographs are routinely used by orthodontists for the planning of treatment for their patients and they can, in some cases, play a decisive role in the early diagnosis of some unexpected medical or surgical disorders. This report presents the case of a substantial dilatation of the upper airway in a 10-year-old girl, which was attributed to a forced Valsalva manoeuvre. The diagnosis was confirmed upon repetition of the teleradiograph with the mouth open.