CT findings in 137 patients with peritoneal carcinomatosis were reviewed to determine the CT signs of pritoneal malignancy. CT of the 20 liver cirrhosis and 17 tuberculous peritonitis were also reviewed to define the differential point between benign and malignant peritoneal change. The results were as follows. 1. The most common primary malignancy encountered in peritoneal carciomatosis was stomach Ca.(50.4%), followed by pancreas Ca.,hepatoma, colon Ca. and ovarian CA. 2. Ascits was the most common CT feature of peritoneal malignancy, present in 99 cases (72.3%). The amount of ascites was voluminous, grade III in 70% of cases and showed high density ascites with average 23 Hounsfield units. 3. Greater omentum involvement was noted in 88 patients, peritoneum in 71 patients and mesentery in 65 paitents. There was no correlation of the primary malignancy type with the incidenceor pattern of the above mentioned site. 4. Bowel wall thickening were observed in 51 patients, among which transverse colon was most frequently involved. 5. Mean attenuation value of ascites in liver cirrhosis was 10.7HU,which was much lower than that of peritoneal carciomatosis. 6. Even though intraperitoneal findings in Tbc.peritonitis showed tendency of relatively small amount of ascites with more predeominat mesenteric change, but the findings of high density ascites, change of peritoneum and omentum etc. were very similar to those of peritoneal carcinomatosis. Therefore, based on only intraperitoneal change, differential diagnosis between them was difficult. 7. False negatives in CT diagnosis of peritoneal carcinomatosis occurred in 7 cases. There were tinynodular changes in intraperitoneal cavity wtihout ascites on operative findings.