Asbestos, a fibrous mineral, has unique physical and chemical properties, including resistance to heat, acids, and other chemicals; flexibility; and great tensile strength. The fibers subdivide into unit fibrils of molecular dimensions, resulting in a vast mineral surface area which has a direct bearing on its unusual features and its numerous applications. Its biological effects, which include fibrogenesis and carcinogenesis, may be related to the cellular reaction, to its large specific surface, or to the size and shape of the fibers. Its oncogenic action may be multiplied by other carcinogens, principally cigarette smoking.There is clinical, pathologic, and epidemiologic evidence that exposure to asbestos, following a long latent period, constitutes an important health hazard. Direct occupational exposure, followed by a long lapsed period after the initial exposure, is associated with pleural plaques and pleural effusion, pulmonary parenchymal fibrosis (asbestosis), pulomonary carcinoma, pleural and peritoneal mesothelioma, and other neoplasms. Indirect exposure may also entail an increased risk of lung disease or mesothelioma or both.Medicolegal investigation of suspected cases includes a lifetime occupational history, clinical history including smoking habits, radiological findings, clinical evidence of asbestosis, and may require detection of asbestos tissue burden.