CONTEXT: - Although many mesotheliomas are related to asbestos exposure, not all are, and there is increasing information on other causes of mesothelioma. OBJECTIVE: - To provide a review of non-asbestos causes for malignant mesothelioma. DATA SOURCES: - Review of relevant published literature via PubMed and other search engines. CONCLUSIONS: - Currently, most pleural mesotheliomas (70% to 90%) in men in Europe and North America are attributable to asbestos exposure; for peritoneal mesothelioma the proportion is lower. In North America few mesotheliomas in women at any site are attributable to asbestos exposure, but in Europe the proportion is higher and varies considerably by locale. In certain geographic locations other types of mineral fibers (erionite, fluoro-edenite, and probably balangeroite) can induce mesothelioma. Therapeutic radiation for other malignancies is a well-established cause of mesothelioma, with relative risks as high as 30. Carbon nanotubes can also induce mesotheliomas in animals but there are no human epidemiologic data that shed light on this issue. Chronic pleural inflammation may be a cause of mesothelioma but the data are scanty. Although SV40 can induce mesotheliomas in animals, in humans the epidemiologic data are against a causative role. A small number of mesotheliomas (probably in the order of 1%) are caused by germline mutations/deletions of BRCA1-associated protein-1 ( BAP1) in kindreds that also develop a variety of other cancers. All of these alternative etiologies account for a small proportion of tumors, and most mesotheliomas not clearly attributable to asbestos exposure are spontaneous (idiopathic).