The change in prevalence in silicosis and pulmonary tuberculosis in black South African gold miners dying from unnatural causes from 1975 to 1991 was studied. Data were analyzed for 16,454 black gold miners. Information on age at death, duration of service, year of autopsy examination, and the prevalence of silicosis and tuberculosis was collected. Analyses were done to assess secular trends in the prevalence of tuberculosis and silicosis, and to determine predictors of the diseases at death. The prevalence of tuberculosis increased from 0.9% in 1975 to 3.9% in 1991. The prevalence of silicosis increased from 9.3% to 12.8%. The prevalence of both diseases increased with age and duration of service. Silicosis was the most significant predictor of tuberculosis (odds ratio [OR] = 1.78, confidence limits [CL] = 1.27 to 2.30). A significant trend for tuberculosis, for year of autopsy, remained after adjustment for the other variables in the model, such as age and duration of service (p = 0.0046). In view of current labor stabilization in the South African mines, one can expect further increases in the prevalence of tuberculosis and silicosis. Lowering of dust levels in the mines is urgently required to prevent the increase of disease burden.