Eight patients with proved gastric carcinoma and 3 with gastric lymphoma were studied preoperatively with computed tomography. CT accurately identified abnormal stomach wall thickening and intra-abdominal tumor extension. Mural thickening was seen on the CT scan when a moderately distended stomach had a wall more than 10 mm thick. CT was useful for assessing surgical resectability, evaluating tumor response to chemotherapy or radiotherapy, and detecting postoperative recurrence. Fourteen patients with an abnormal barium study suggesting gastric malignancy were also studied with CT, which correctly demonstrated a normal stomach or identified the reason for the abnormal barium study, such as an unusual placed spleen or a pancreatic carcinoma invading the stomach.