To obtain complete establishment of all fatal cases of primary malignant mesothelioma (PMM) known to pathologists in Canada from 1960 to 1975 and in the United States (US) for 1972, data derived from published and unpublished surveys were consolidated and examined. Consideration was given to the epidemiologic interpretation and to etiologic factors. The results were discussed in regard to sex, age, and tumor site; incidence by age, sex, and geographic region; probability of occupational exposure to asbestos (1332214) for patients and referents; home exposure of patients and referents to the dusty clothing of asbestos workers; neighborhood exposure of patients and referents without occupational or domestic exposure; correlation of tumor site and occupation for patients and referents; exposure of patients and referents to dust from fiberglass (14808607), cement, rubber, copper (7440508), nickel (7440020), and wood; and cigarette smoking habits of patients and referents. Of the 395 male cases reported to the end of 1972, 78 and 22 percent were pleural and peritoneal, respectively; 61 and 39 percent of the female cases were pleural and peritoneal, respectively. Incidences of accepted cases of PMM differed little in three regions of Canada; rates for males in the US were highest in the Pacific and Mid Atlantic regions. The highest relative risk (RR), 46.0, was found in males employed in insulation, followed by asbestos production and manufacturing and the heating trades other than insulation, with RR values of 6.1 and 4.4, respectively. Eight subjects, but no referents, had been exposed at home to the dusty clothing of an asbestos worker. Excluding persons with occupational or domestic exposure, one US case had lived within 20 miles of a chrysotile (12001295) mine. Over half of male cases with pleural or peritoneal PMM had been employed in one of the five occupational groups having recognized association with PMM. Exposure to other dusts and cigarette smoking habits appeared not to be etiologic factors.