The main characteristics of the International Labour Office (ILO) International Classification of Radiographs of the Pneumoconioses (1980) are reviewed. Applications to epidemiological, research, and clinical problems are outlined. The need for multiple readings, reading protocols and appropriate administrative arrangements is emphasized. Possible improvements to the Classification are discussed. The basic descriptive features of the scheme are distinguished from supplementary interpretative facilities; it is suggested that misuse of the Classification occurs primarily when these two functions are confused.