We evaluated the preoperative CT findings in 10 patients with colon carcinoma in whom peritoneal metastases had been surgically confirmed. Seven patients lacked ascites. No CT findings suggestive of peritoneal metastasis were observed in two patients without ascites even by retrospective evaluation. A large mass was observed in the cul-de-sac in another. In the remaining four patients, small peritoneal metastases ranging from 8 to 11 mm in diameter were observed at the omentum in two, along the falciform ligament in one, and at both the omentum and the iliac fossa in one; three of these patients had received no prospective diagnosis of peritoneal metastasis prior to the surgery. In patients with advanced colon carcinoma with suspected serosal invasion, the entire peritoneal cavity should be carefully examined and interpreted using CT in order to detect small peritoneal implants even when ascites is absent.