The prevalence of silicosis in the migrant laborer in the South African, Orange Free State gold mines has not previously been estimated. Two methods were used to estimate the prevalence of silicosis in this population. The two techniques are described. The difference between the two estimates illustrates the difficulty of epidemiologic studies in this type of working population. It is noted that the highest estimate of 138 cases per 10,000 workers is certainly less than the true prevalence of the disorder. The use of routine miniature (100-mm) chest radiographs for the detection of silicosis was validated through comparison with normal size (125-kV radiographs and through analysis of the consistency of reading of second miniature films from the same subjects.