The author reviewed 1, 517 human malignant mesothelioma cases from 1975 through August 2000. These mesothelioma cases were definite or probable in diagnostic certainty. Sources of these cases varied including asbestos insulation workers, UNARCO workers, Cancer and Leukemia B mesothelioma panel cases and random cases. Pathology materials consisted of autopsy, biopsy and rare cytology specimens. 92.3% of these patients were male, and 85.8% were between 50 and 79 years in age. The major primary site of the tumor was the pleura (73.1%). However, in a group of the asbestos insulation workers, the peritoneum was the more common primary site of malignant mesothelioma, compared to the pleura. Histologically, epithelial cell type was the majority (61.1%), followed by biphasic (22.1%) and fibrosarcomatous (16.4%). A double primary tumor (malignant mesothelioma associated with other cancer) was present in 32 of the 1, 517 cases. These 32 cancers included lung cancers, renal cell carcinomas, colorectal cancers, pancreatic cancers and a cancer of the larynx, which are known to be at higher risk among asbestos insulation workers. The latency period of the vast majority (98.1%) of these mesothelioma cases were longer than 20 years. It is well accepted that cigarette smoking does not contribute to the induction of malignant mesothelioma. Indeed, the present study confirmed that 19.9% of these mesothelioma patients had never smoked cigarettes.