The clinical and diagnostic significance of abdominal computed tomography (CT) was evaluated in 123 patients with primary gastric adenocarcinoma and disseminated peritoneal metastases. The peritoneal metastases were diagnosed by CT findings such as ascites (30.1%), wall thickness of the intestine (1.6%), increase in fat density of peritoneal fat tissue (4.9%), peritoneal nodules (2.4%), and hydronephrosis (4.9%). The overall diagnosis of peritoneal metastasis was 37.4%. The CT findings of peritoneal metastases were significantly correlated with anemia, poor performance status, distant metastases, P3, and resectability of the primary tumor. The survival of the patients with positive findings was significantly poor (150 days of median survival), compared with those without findings (230 days). The abdominal CT thus provides information for diagnosis of peritoneal metastases and on the prognosis in patients with primary gastric cancer.