Information on radiographic evidence of coal workers' pneumoconiosis (CWP) is presented for a group of 3,194 underground bituminous coal miners and ex-miners examined between 1985 and 1988. Prevalence of CWP was related to estimated cumulative dust exposure, age, and rank of coal. On the basis of these data, miners of medium to low rank coal, who work for 40 years at the current federal dust limit of 2 mg/m3, are predicted to have a 1.4% risk of having progressive massive fibrosis on retirement. Higher prevalences are predicted for less severe categories of CWP. Miners in high rank coal areas appear to be at greater risk than those mining medium and low rank coals. Ex-miners who said that they left mining for health-related reasons had higher levels of abnormality compared to current miners. Data Collection Methods: A large epidemiological study, denoted the National Study of Coal Workers' Pneumoconiosis (NSCWP), was begun by the U.S. Public Health Service These results comprise information from this study on prevalence of coal workers' pneumoconiosis (CWP) and its relationship with dust exposure. Initially, 31 underground mines around the country were visited by a mobile examination trailer staffed by a medical team. Radiological data, information on ventilatory function and respiratory symptoms, and data on work and smoking history were obtained on over 9,000 active miners. This first round of the study was followed by similar second and third rounds of medical surveys of active miners at Division of Respiratory Disease Studies, NIOSH, at essentially the same mines at roughly 5-year intervals. The data presented here are drawn from the most recent (1985-1988) round of surveys, i.e., Round 4, a follow-up study of selected Round 1 and Round 2 participants. Many of the miners in the studied cohort had started work in coal mining around 1970. Much, if not all, of their mining tenure therefore coincides with the period when dust levels were mandated to be 3 mg/m3 (1970-1972) and 2 mg/m3 (1972 onwards) [Coal Mine Health and Safety Act, 1969]. These levels compare to dust concentrations of 6 mg/m3 or more for face workers recorded before 1970 and applicable to a previous exposure-response analysis of CWP. The results given in this report therefore not only provide further information on exposure-response, but also supply information pertinent to miners working in current coal mining conditions. View detailed descriptions of the methods.