[en] Adenoid size and nasopharyngeal airway can be assessed both clinically and radiologically. Recent emphasis has been placed on the measurement of the nasopharyngeal airway using lateral radiographs of the nasopharynx. This method may be inaccurate for technical reasons. This paper is presented in two parts: in the first part, the errors are considered theoretically; and in the second part, the effect of these errors is considered in radiographs taken specifically to measure the nasopharyngeal airway. (author)