CT findings in 137 patients with peritoneal cacinomatosis were reviewed to determine the CT signs of peritoneal malignancy. CT of the 20 liver cirrhosis and 17 tuberculous peritonitis were also reviewed to define the differential point between bening and malignant peritoneal change. The results were as follows. 1. The most common primary malignancy encountered in peritoneal carcinomatosis was sto-mach Ca. (50.4%) followed by pancreas Ca, hepatoma, colon Ca. and ovarian Ca. 2. Ascites 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 note in 88 patients peritoneum in 71 patients and mesentery in 65 patients. There was no correlation of the primary malignancy type with the incidence or pattern of the above mntioned site, 4. Bowel wall thickenings were observed in 51 patients among which transverse colon was most frequently invoved. 5. Mean attenuation value of ascites in liver cirrhosis was 10.7 HU which was much lower than that of peritoneal carcinomatosis. 6. Even though intraperitoneal findings in Tbc. peritonitis showed tndency of relatively small amount of ascites with more predominant mesnteric 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 tiny nodular changes in intraperitoneal cavity without ascites on operative findings.