The extent of the pneumoconiosis problem in the Pennsylvania bituminous coal industry has been under discussion for some time. Some believe that there is a problem and others deny its existence. A satisfactory answer to this question cannot be found in the literature. Therefore, more than 16,000 working and retired coal miners in the central and western Pennsylvania bituminous coal districts were screened over a 3-year period. An occupational, personal history, vital capacity, and 14-by-17-in chest xray were obtained on each man. In the study of over 5,000 bituminous miners in central Pennsylvania, 34% were found to have roentgen evidence of pneumoconiosis, whereas 14% of the 10,000 western Pennsylvania bituminous miners studied showed such evidence.