A case of diffused malignant mesothelioma of the peritoneum in a 64-year-old man is presented. This mesothelioma, of the papillary type, was complicated, after a year without significant clinical symptoms, by the development of ascites and obstructive upper bowel ileus. Physiological-anatomical and clinical aspects, as well as special radiologic findings and therapeutic regimens, are discussed in the light of the literature. It is recommended that all patients with malignant mesothelioma of the peritoneum be treated by total abdominal irradiation and intreperitoneal instillation of colloid P32.