A questionnaire was sent to institutions responsible for matters of pneumoconioses in a number of countries exploring the present use and trends for further development of the International Labor Office (ILO) Classification. In almost all of the countries surveyed (Australia, Austria, Belgium, Brazil, Canada, Chile, China, Czechoslovakia, Denmark, Egypt, Finland, France, German Democratic Republic, Greece, Indonesia, Mexico, Netherlands, Nigeria, Norway, Peru, Poland, Rumania, Spain, Sweden, Uganda, USSR, United Kingdom, United States of America, and Yugoslavia) a standardized classification of pneumoconioses was used for general or for specific purposes. There were exceptions in a few countries in which pneumoconioses appeared to be very rare diseases due to the limited extent of industries involving exposure of workers to fibrogenous mineral dust. In view of their principal use and the compensation of the disease, the national classifications sometimes slightly modified the ILO Classification or included additional criteria. Therefore, a clear distinction must be made between the national classifications of pneumoconioses as diseases, and the international classification of radiographical appearances of pneumoconioses. This review also considered the qualification of readers and organization of reading of radiographs as well as offered suggestions for further development of the ILO Classification.