A 49-year old man underwent an operation for pneumothorax, during which a tiny tumor on internal surface of the thoracic wall was extirpated. As the tumor proved to be malignant mesothelioma postoperatively, it was planned to be followed up strictly after discharge, but the patient did not visit for 6 months after discharge. When he was admitted again because of cough and fever, the mesothelioma had already disseminated diffusely in the whole thoracic cavity. So he underwent total pleuropneumonectomy, but died 49 days after operation.