RESUMEN
Introduction: Plain radiographs are still routinely used for diagnosis in dentistry. They allow the assessmentof anatomical structures and their variations, and the detection of abnormalities in the region assessed. Theaim of this research was to determine the width and height distances of the frontal sinus on posteroanteriorskull view of Brazilian subjects. Materials and methods: The sample was composed of 158 posteroanteriorfacial radiographs (Caldwell projection). It was measured the height and width of the frontal sinus, both sides,under a standardized protocol, using rules and a viewer box. The relationship between frontal sinus size andside of the face, and size and age were evaluated. Results: Thirteen radiographs were excluded (six of unilateralfrontal sinus, two agenesies, and five showing totally individualized chambers). The final sample studied was of145 subjects. The mean values obtained were a 68 mm for latero-lateral and 39 mm for superoinferior distances.In 39.3% cases both sides were approximately equal or had the left chamber larger than the right one. Therewas a significant correlation between width and height of frontal sinus (Spearman coefficient), however therewas no significant difference among the age groups studied (Kruskal-Wallis, p > 0,05). Conclusion: There is agreat anatomical variety of frontal sinus in this population. The left cavity of frontal sinus is larger or equal tothe right one and the age group differences was not significant regarding the size of the frontal sinus.