Throughout the 20th century, asbestos was one of the most widely used carcinogens to which workers were exposed in the workplace; non-occupational exposure is also significant for many populations. There is a wide disparity in the incidence of pleural mesothelioma (of which asbestos is the primary cause) across different parts of the world, but in most populations, it is higher among men, and manual laborers have by far the highest incidence, thus demonstrating the importance of occupational exposure. A higher incidence is observed in industrialized countries due to the long history of asbestos use. Although the production and commercial use of asbestos have almost completely ceased in the United States and Europe, the incidence of mesothelioma appears to be stabilizing or increasing in most of these countries due to the long latency period of this disease (20–45 years). Today, in many Western countries, occupational exposure to asbestos has generally decreased, unlike in many less developed countries where high levels of exposure are common. The risk of pleural mesothelioma following non-occupational exposure to asbestos (domestic sources, living near an industrial or natural source of asbestos) appears to be established. (R.A.)