Clinical, radiographic, surgical, and pathologic findings and survival in 92 patients with diffuse malignant mesothelioma (DMM) of the pleura who were examined at the Mayo Clinic between 1950 and 1980, were studied retrospectively. With the use of defined criteria and ordinary tissue stains, the 92 cases were classified into the following histologic subtypes: purely epithelial, 42 cases; mixed, 29 cases; and sarcomatous, 21 cases. Eight of the sarcomatous cases were desmoplastic. Median survivals were 12, 5, and 3 months for the patients in the epithelial, mixed, and sarcomatous groups, respectively. Survival was significantly longer for patients with epithelial DMM. Women survived longer than men but more often had epithelial DMM. Early disease manifested as multiple discrete pleural nodules, predominantly on the parietal pleura. However, nine patients had a dominant mass. Radiographic signs especially suggestive of DMM were nodular pleural thickening, irregular thickening of interlobar fissures, a dominant mass, or decreased volume of the affected hemithorax.