One hundred normal Cnldwell view radiographs were examined on patients who had no signs or symptoms referable to the frontal sinuses. Magnification factors were determined for Caldwell views obtained on a dedicated head unit and ns part of a skull series. The areas of the frontal sinuses were actually measured with a Zeiss Videoplan 2 computer and corrected for magnification. The area variation in this normal population was determined. Four linear measurements were individually correlated with these areas. Two of these lines had excellent correlation with the sinus area and if either of these lines exceeds a calculated value, the sinus area exceeds the 99th percentile of the normal population and can be considered abnormally enlarged. This technique provides a rapid, easy, and reliable method for assessing abnormally enlarged frontal sinus areas.