PURPOSE: To evaluate the diagnostic accuracy of chest x-ray interpretation of diffuse calcification of pulmonary nodules. MATERIALS AND METHODS: On plain chest radiograph and CT, 152 pulmonary nodules with diffuse calcification in 98 patients were selected. The nodules were of various diameters : 44 were of 0.5 - 1cm (Group1), 58 were of 1 - 2cm (Group 2), and 50 were of 2 - 3cm (Group 3). On plain chest radiograph, diffuse calcification was considered to be present when the density of pulmonary nodules of 0.5 - 1cm and 1 - 2cm indiameter was greater than that of the overlapping area of the second and fifth ribs. The density of nodules 2-3cmin diameter was compared with that of the mid-claviclar cortex; calcification was considered to be present when the density of the former was greater than that of the latter. Diffuse calcification of a pulmonary nodule on CT image was considered to be present when more than 10% of the area of the nodule showed a higher attenuation than the surrounding rib cortex. RESULTS: The overall diagnostic accuracy of chest radiographs in the detection of diffuse calcification was as follows : sensitivity 77.6%, specifity 89%, PPV (positive predictive value) 82.3%, NPV(negative predictive value) 86.9%. In group 1, sensivity was 96%, specifity 89.5%, PPV 91.6%, and NPV 94.9%. In group 2 nodules, sensitivity was 77.8%, specifity 91%, PPV 89%, and NPV 81.4%. In group 3, sensitivity was 56%,specifity 88% PPV 56% and NPV 83.9%. CONCLUSION: Chest radiographs showed relatively high accuracy in the diagnosis of diffuse calcificatio of pulmonary nodules, particulary when the nodule was less than 2cm in diameter. As the nodule increased in diameter, diagnostic accuracy declined.