AbstractUntil the publication of a report by Wagner et al. in 1960 (1) describing 33 cases of diffuse pleural mesothelioma in South Africa, this tumor was considered a clinical rarity. Since then, the relevant medical and epidemiological literature has grown substantially, with recent reports providing evidence that the incidence of this tumor has been increasing steadily. This increase has been particularly striking among asbestos-exposed occupational cohorts.Several issues have complicated epidemiological studies of diffuse pleural mesothelioma as well as hindered the recognition of malignant mesothelioma as a distinct pathological entity. Among these are the rare occurrence of this malignancy in the early part of this century; the existence of two forms of the tumor, namely the localized and benign versus the diffuse and malignant; and the contention that apparently primary tumors of the mesothelium may actually be metastases from a primary tumor located elsewhere in the body (2). Over the last 40 years its increased occurrence and the implication of asbestos as an etiologic factor have resulted in the standardization of diagnostic criteria and acceptance of mesothelioma as a distinct neoplasm (3).