The influence of body shape on progressive massive fibrosis (PMF) in coal miners was examined. Data obtained in a 20 year study of the incidence of simple pneumoconiosis (SP) and PMF in coal miners living in the Rhondda Fach and Aberdare Valley, Wales, the United Kingdom were examined. The data included assessments of SP severity denoted by a five point scale running from 1 to 3 as determined from chest X-rays, the presence or absence of PMF, age, height, weight, body mass index (BMI), mean chest diameter (MCD), and body type, defined as body height squared divided by 10 times the MCD. The data were analyzed by ten logistic regression models to assess the effect of the anthropometric parameters, SP category, presence or absence of pulmonary tuberculosis, living in Rhondda Fach and Aberdare Valley, and age on the risk of developing PMF. Subjects who developed PMF had consistently lower mean body weights than those who did not. BMI and body type had little influence on PMF risk. All models predicted that SP category and to a lesser extent body weight had significant influences on the risk of developing PMF. Age, residence, and pulmonary tuberculosis were not significant risk factors. The model that gave the best fit with the data predicted that for subjects with category 1, 1.5, 2, 2.5, or 3 SP the predicted number of PMF cases were 0.024, 15.991, 49.006, 55.000, and 73.002, respectively. The number of observed cases was due to body weight was 0.02, 7.2, 14.7, 18.3, and 29.8%, respectively. The author concludes that higher grades of SP and reduced body weight are significant risk factors for PMF. Pulmonary tuberculosis does not appear to be a significant risk factor. If reduced body weight can be validated as a risk factor for PMF, a weight monitoring program may be important for protecting the health of coal miners.