The authors present data of the clinical X-ray and morphological diagnostics of malignant gastric ulcers revealed in 96 patients. The total number of patients with gastric ulcer operated upon was 642. The morphological findings may serve the only reliable criterium of malignancy. Results of the operative treatment of such a malignant ulcer of the stomach are dependent on the spread of malignant invasion in the gastric wall. Treatment of patients with the involved mucosa only gave 5-year survival in 89.5%. Spread of the malignant invasion throughout the whole thickness of the gastric wall--50.0%. In patients with metastases into lymph nodes (independent of the invasion into the gastric wall) 5-year survival made up 29.4%.