Twelve cases of pathologically proved pleural mesothelioma collected from 1983 to 1987 were analyzed retrospectively. There were 9 males, and 3 females, aged 14-76 year-old (mean 54 year-old). Eight cases were malignant mesothelioma. Four cases were benign mesothelioma. The male to female ratio in malignant tumor was 1 to 7; in benign tumor it was 1 to 1. The mean age in malignant mesothelioma was 45 year-old, and in benign mesothelioma it was 58. Of the 8 cases with malignant mesothelioma, there were 2 cases (25%) of fibrous type, 1 case (12.5%) of epithelial type, and 5 cases (62.5%) of mixed type. Asbestos exposure history was not evident in our series. Definitive diagnosis was obtained in 10 cases by thoracotomy (83%). Two cases of malignant mesothelioma were verified by pleural biopsy. The diagnostic yield is 40% for pleural biopsy, and 100% for thoracotomy. Bronchoscopic examination, percutaneous biopsy, and pleural effusion analysis were useless in making a definitive diagnosis and distinguishing from metastatic adenocarcinoma in our opinions.