The prevalence of pneumoconiosis and its relationship to dust exposure in a cohort of US coal miners were examined. Data collected on 3,194 underground bituminous coal miners and exminers, who were alive and 58 years old or younger in 1985, during the National Study of Coal Workers Pneumoconiosis (CWP) (NSCWP) were utilized. NSCWP was an ongoing epidemiological study of respiratory health status of US coal miners that was started in 1970. The NSCWP database consisted of chest X-ray, ventilatory function, respiratory symptomatology, and dust exposure data and work and smoking histories. The miners were followed through round 4 of the study, 1985 to 1988. The incidence of simple CWP, category 1 (CXP1) and category 2 CWP (CWP2) and progressive massive fibrosis (PMF) was determined from the chest X-rays using 1980 International Labor Office criteria. Associations between the various categories of CWP and PMF and cumulative coal dust exposure, age, and the rank of the coal being mined were examined by logistic regression techniques. During round 4, 53% of the cohort were current miners. Approximately 33% had been laid off because of a recession. The remaining 14% had left mining for health reasons. Cumulative coal dust exposures ranged up to 211 milligram years per cubic meter (mg-yr/m3), with 75% of the exposures lying between 13 and 41mg-yr/m3. The prevalence of the various grades of CWP was significantly positively associated with cumulative coal dust exposure, age, and coal rank. Representative data indicated that for 58 year old miners who had mined low to medium rank coal for 40 years and were presently exposed to 2mg/m3 coal dust, the risks of CWP1, CWP2, and PMF expressed as the predicted prevalences were 14, 3.1, and 1.4%, respectively. If these miners had mined high rank coal under the same conditions, the risks for CWP1, CWP2, and PMF were increased to 25, 8.9, and 5.1%, respectively. The risks of developing CWP1, CWP2, and PMF were greater in workers who left coal mining for health reasons than in current miners. The authors conclude that although CWP is currently occurring at lower rates than previously due to reductions in coal dust exposures, the present coal mining workforce is still at risk for developing CWP over a working lifetime.