The progression of silicosis was measured for 631 South African gold miners to determine the effect of silica dust exposure on the rate of progression of simple silicosis and the development of progressive massive fibrosis (PMF). Silicosis was found to be a progressive disease regardless of whether exposure was continued after onset (94.6% progressed) or not (88.3% progressed). Cumulative dust exposure was significantly associated with the rate of progression (p = 0.0014). When dust exposure before and after onset was considered, it was found that exposure after onset was significantly associated with progression (p = 0.0001) whereas dust exposure before onset was not (p = 0.95). Silicotics developing PMF had more exposure after onset of simple silicosis than silicotics who did not develop PMF. Progression appears to slow as the category of profusion increases; however, this cannot be stated with assurance given the study design used. The data suggest that the removal of silicotics from continued dust exposure will reduce the rate of progression of silicosis as well as the risk of developing PMF. It is also speculated that individual susceptibility to develop silicosis may not be related to the susceptibility to progress.