Mild to severe dysplasia ranked first among precancerous lesions in gastric adenoma and stomach stump gastritis. Repeated gastric biopsy of adenomas revealed enhancement of dysplasia proceeding to papillary adenocarcinoma. Epithelial dysplasia invariably occurred in areas adjacent to early carcinoma. A relationship was established between the pattern of dysplasia and histologic type of cancer. As dysplasia advanced, the ultrastructural signs of cell atypia became more pronounced. The electron microscopic features of severe dysplasia were similar to those of carcinoma.