In summary, the radologic appearance of peritoneal carcinomatosis and sarcomatosis is best understood with a thorough knowledge of the natural history of the disease. Computed tomography (CT) examinations of the abdomen and pelvis are insensitive to small volumes (< 5 cm) of diffuse peritoneal seeding. However, when larger volumes of peritoneal tumor are present, CT can be helpful defining the patients who are good candidates for complete cytoreduction (no small bowel disease) from those who are less likely to have a complete cytoreduction (extensive small bowel disease with clumping and obstruction). Thus CT examination plays a critical role in the identification of patients with mucinous tumors who are operative candidates. Further research is needed to improve sensitivity and in the monitoring of recurrence in patients with gastrointestinal cancer.