A study of the prevalence of coal worker's pneumoconiosis (CWP) and pulmonary function in Chilean coal miners was conducted. The cohort consisted of 1905 active or retired Chilean coal miners, mean age 45.4 years, with an average of 20.6 years of underground mining experience. Most of the retired miners were claimants for occupational disease benefits. Chest X-rays were made and read for evidence of CWP using the 1971 International Labour Organization system. Pulmonary function testing was performed. The subjects completed a respiratory symptom questionnaire. Approximately 29% of the subjects were smokers, of which only 1.7% were heavy smokers. Approximately 20.8% of the miners had evidence of bronchial obstruction, 1% restrictive ventilatory insufficiency, and 41.6% chronic bronchitis. Only 3.6% of those with bronchial obstruction had an abnormal 1 second forced expiratory volume (FEV1) reading, defined as being less than 80% of normal. A total of 424 miners had radiographic evidence of CWP, 29.2% with noted bronchial obstruction. The prevalence of bronchial obstruction in those with normal chest X-rays was 13.6%. The difference was statistically significant only for 50 to 59 year old miners. The prevalence of progressive massive fibrosis was 0.22%. The percentage of miners with abnormal FEV1s, forced vital capacity (FVC), or FEV1/FVC ratios did not vary significantly with CWP severity. Values of mean forced expiratory flow at 25 to 75% of FVC and total pulmonary capacity decreased with increasing severity of CWP. The authors conclude that the prevalence of CWP in the cohort is influenced by the group of retired miners seeking disability benefits. Impairment of bronchial airflows does not appear to be an important etiological factor for the development of CWP.