The present study examines the association between asbestos-related pleural plaques and lung function in a group of workers with occupational exposure to asbestos. Exposure, smoking, and respiratory histories, chest radiographs, flow-volume loops, and single breath DLCOs were obtained on 383 railroad workers. A score based on the ILO-1980 classification system was used to quantify the extent of plaquelike thickening. In order to eliminate potential confounders, we excluded from final analysis subjects with diffuse pleural thickening (n = 10) or small irregular opacities classified as profusion 0/1 or greater (n = 6) on chest radiograph. Definite pleural plaques were observed in 22.6%. The single breath DLCO was similar in the groups with and without plaques (p = 0.0550). Decrement in FVC and the occurrence of pulmonary restriction were associated with the presence of definite plaques (p = 0.0306 and 0.0431, respectively) and with quantitative pleural score (p = 0.0135 and 0.0126), controlling for duration of asbestos exposure and smoking. A test for trend revealed an association between level of diagnostic certainty (none, suspect, definite) for pleural plaques and these measures of lung function (p less than 0.02). Our findings reveal an association between asbestos-related pleural plaques and decrement in lung function as measured by FVC and criteria for pulmonary restriction.