Thickened gastric walls of diffusely low attenuation were observed on CT of three of eight patients with mucinous adenocarcinoma in a retrospective review of 141 cases of gastric carcinoma. On pathologic examination the low attenuation correlated with large amounts of mucin in the pathologic specimens. Mucinous adenocarcinoma with abundant mucin should be included in the differential diagnosis of thickened gastric walls of diffusely low attenuation.