Background: Lymph node metastasis in squamous cell carcinoma of the esophagus is rare, and the cancer remains in the lamina propria mucosae. In cases with cancer invading the muscularis mucosae (MM), the incidence of lymph node metastasis is approximately 7%. For endoscopic treatment of mucosal cancer, it is necessary to diagnose cancer invasion into the MM. The aim of this study was to estimate cancer invasion into the MM by esophagography. Methods: One hundred ten lesions of the slightly depressed type were classified into two groups: in group A, cancer was confined to the lamina propria mucosae; in group B, the cancer invaded the MM or slightly into the submucosa. Radiologic findings of each group were studied. Results: In group A, 69% of 70 lesions showed mild depression and a smooth or undulated surface. Thickened folds were noticed in only 3%. In group B, 83% of 40 lesions showed mild or moderate depression with well-defined granules. Thickened folds were evident in 78%. In the differentiation between groups, the accuracy rates of each finding of moderate depression, well-defined granules, and thickened folds were 85%, 73%, and 90%, respectively. The overall diagnostic accuracy rate was 90%. Conclusion: Esophagography is useful for estimation of cancer invasion into the MM and, hence, the decision to apply endoscopic treatment to mucosal cancer.