Abstract Aim: The aim of this study was to assess the added value of computed tomography (CT) with ultrasound in identifying unresectable or incurable gastric cancer. Methods: One hundred and eighteen patients with various types of gastric cancer were preoperatively staged with ultrasound and CT between January 1999 and October 2000. Each individual was evaluated for ascites, liver metastasis and peritoneal metastases. The observations were compared to findings at surgery. Results: Both techniques were highly specific (93–99%) for all conditions except retroperitoneal invasion (85%). The sensitivities of ultrasound and CT were 64 and 36% for ascites, 50 and 62% for liver metastasis, 9 and 13% for peritoneal metastasis and 18 and 41% for retroperitoneal invasion. Ultrasonography was more sensitive than CT for detecting ascites, and CT was better for detecting retroperitoneal invasion. Conclusions: Both techniques allowed more accurate identification of liver metastasis and ascites than peritoneal metastasis and retroperitoneal invasion. In order to simplify scanning of patients with gastric cancer, we recommend that CT investigation should be done only in cases where the ultrasound findings are suspicious.