To clarify the usefulness of screening ultrasonography (US) to diagnose gastric and colorectal cancer, patient records were analyzed retrospectively.,Ultrasonography was performed for patients with abdominal symptoms. They were then subjected to computed tomography (CT) when diagnosed with gastric cancer, colorectal cancer, or bowel obstruction. Patient records were analyzed retrospectively after final diagnosis of gastric cancer or colorectal cancer by endoscopy, surgery or necropsy.,Twelve patients were diagnosed with colorectal cancer and six with gastric cancer. The detailed structure of colorectal cancer was visible as wall thickening with US, while cancer was often illustrated as a mass by CT. Loss of stratification was clear with US in 11 patients. US demonstrated wall thickening in 10 patients and a mass in 1 patient, while CT demonstrated wall thickening in 3 patients and a mass in 8 patients. The structure of colorectal cancer was more obvious when using US than when using CT. One patient demonstrated focal wall thickening with US, but this was not detected by CT.,US is useful for diagnosis of gastric cancer and colorectal cancer. US produces more detailed findings in colorectal cancer than CT.