Asbestos pleurisy is relatively uncommon among patients who present with pleural fluid. Association of diffuse malignant mesothelioma with asbestos pleurisy has not been reported in Japan, although 10 cases have been reported in the world literature. We encountered a 51-year-old man in whom diffuse malignant mesothelioma developed during a 5-year course of asbestos pleurisy. Mesothelial cells in patients with asbestos pleurisy are likely to be exposed to asbestos for a long time, which may increase the risk that mesothelioma will develop.