One or more bronchi are visualized end-on roentgenographically in the parahilar zone of the PA chest and theyrange in diameter from 3 to 7mm. Thickening of bronchial walls visualized end-on is an occasional roentgenographicmanifestation of certain diseases notably chronic bronchitis, diffuse interstitial lymphoma and interstitialpulmonary edema. We reviewed PA chest films of some 727 normal subjects and 371 cases of silicosis seen at theDepartment of Radiology, St. Mary's Hospital, Catholic Medical College during the year 1979. Of these, we sample30 cases each for matched age groups, both normal and silicosis subjects, in which bronchial wall were clearlyvisulaized at parahilar zones. Thus, a total of 180 cases were assessed of the thickness of bronchial wall and theraio of wall thickness to outer diamter of bronchi. The following results were obtained; 1. The mean of the outerdiameter of the bronchi of the normal subjects was 5.32±1.21mm, and 5.31±0.92mm in silicosis. No significantdifferences were noted between two groups and each age groups. The bronchi measuring 2.5-5.0 mm in size were mostprevalent in both normal and silicotic subjects. 2. As to bronchial wall thickness, the mean of the normal andsilicosis subjects were 0.81±0.34mm, and 1.19±0.41 mm, respectively. The bronchial wall measuring 0.5 mm inthickness as most prevalent in the normal subjects and 1mm in silicosis. The difference was significant(p<0.001).3. In ratio of wall thickness to outer diameter was 0.15±0.06 in the normal subjects and 0.22±0.07 in silicosis,respectively. The difference was significant(p<0.001).