The occurrence of symptoms due to pleural plaques was studied by means of a questionnaire administered to asbestos-exposed workers participating in a health-screening program. One hundred thirty subjects who were found to have pleural plaques were compared with 1,103 control subjects who had no plaques and showed no changes on x-ray examination. No difference in occurrence of thoracic pain was found between the two groups. Dyspnea was more common among patients with pleural plaques, who also tended to have lower lung function values. There was a good correlation between reported dyspnea and lung function. The increased number of complaints of dyspnea among patients with pleural plaques could not be explained by differences in age or in smoking habits. It is suggested that dyspnea in patients with pleural plaques is caused by sub-roentgenologic fibrosis.