Miners from the US National Study of Coal Workers' Pneumoconiosis (NSCWP) who reported clinically significant declines in 1 second forced expiratory volume (FEV1) were identified, and possible risk factors for these declines were investigated. The NSCWP assessed the respiratory health status of underground miners in the US via spirometry and questionnaire surveys. This study occurred in four rounds (R1, R2, R3, R4) and covered workers from 35 mines. Miners common to the NSCWP study rounds R1 and R3, R1 and R4, or R2 and R4 were grouped into cells according to age, height, initial FEV1, and smoking status. For all cells containing two or more individuals, the miners with the greatest and lowest annual FEV1 decline were paired. This process continued until no more pairs could be selected, and yielded 141 pairs from R1 to R3, 68 pairs from R1 to R4, and 165 pairs from R2 to R4. Miners were removed if they were selected more than once as both a case and a referent, and also if no acceptable flow volume spirometry curves were available. The Statistical Analysis System was used for data analysis and descriptive statistical analysis of data from cases and referents was performed using both group and matched pair comparison approaches. Age, sex, race, height, weight, FEV1, forced vital capacity (FVC), FEV1/FVC%, years of mining and underground mining experience, mine region distribution, age started mining, interim respirable dust exposure, and smoking status were analyzed. Cross sectional analyses of initial and final FEV1, FVC, FEV1/FVC% showed that increasing age and smoking habits were associated with lower lung function in both cases and referents. Cough, phlegm, bronchitis, dyspnea, wheezing, and emphysema were more prevalent in cases than in referents. Mining tenure was positively associated with a significant decline in lung function. The authors conclude that declines in FEV1 in miners were associated with coal mine exposure, mining region, and initial symptoms of cough and phlegm.