The classification for pneumoconiosis which was developed by International Labour Office(ILO) on the basis of Radiological findings of simple chest radiography has been widely used for the study and diagnosis of pneumoconiosis. But many problems have been revealed during the pneumoconiosis study using this classification. Those problems come from simple radiography itself or classification systems. Among those, inter-reader and intra-reader variability are the severest problems, even though many efforts have been devoted to lessen the variability. With introduction of computed tomography (conventional CT and HRCT), we are learning many new aspects about the occupational lung diseases, especially pneumoconiosis. So the studies for pneumoconiosis using tomography are reviewed, focusing on silicosis, coalworkers' pneumoconiosis, and asbestosis. But in our country, the studies of that kind are very scant. It is necessary to study and diagnose pneumoconiosis by CT, because that is the need of workers and the responsibility of physicians working in the field of occupational medicine. CT is superior to simple radiography in early detection, determination of severity, and follow-up of pneumoconiosis. But simple radiography is and should be the main method for the study and diagnosis of pneumoconiosis. Although, because of radiation hazard, cost, time, and geographical availability, the method can not and should not be used on the routine basis, we have to consider the use of CT, if possible and if necessary. Before using CT widely, we should develop the standardized criteria regarding to scanning methods and reading criteria. If not, the same problems as those of simple radiography will be occurred, and then there will be no progress in occupational medicine and workers' health.