We reviewed 354 cases of malignant diffuse mesothelioma (MM) in women from a database of 2858 histologically confirmed MM cases. There was a pleural predominance with 78% pleural MM and 22% peritoneal MM. The pleural tumors consisted of 72% epithelioid, 19% biphasic, and 9% sarcomatoid variant. The peritoneal tumors consisted of 82% epithelioid, 13% biphasic, and 5% sarcomatoid. The immunohistochemical profile was typical of what is well-accepted and previously described for MM. When examining tumor subtype and location, there was a trend toward epithelioid subtype and peritoneal location; however, this did not reach statistical significance. Age at the time of diagnosis ranged from 19 to 93 years with a mean of 60 years. The median age at time of diagnosis for pleural MM was 65 years and for peritoneal MM was 52 years. A further look at age and histologic subtype showed no statistically significant difference in age between MM subtypes. Survival was greatest for epithelioid variant, and this was magnified in the peritoneum. A majority of our cases were exposed to asbestos through a household contact. Asbestosis and parietal pleural plaque were present in 5% and 50% of cases with data, respectively. Fiber analysis data was available in 67 cases; 38 cases had elevated asbestos fiber burden, and tremolite was the most common asbestos fiber type detected. Commercial and noncommercial amphibole asbestos fibers were elevated in nearly equal numbers of cases.