All gastric ulcers diagnosed during the period November, 1969-May, 1974, were prospectively evaluated by roentgenography, fiberoptic gastroscopy, directed biopsy, and brush cytology. Gastroscopy was performed routinely in patients with radiologic diagnosis of gastric ulcer or questionable findings, and in symptomatic individuals with negative roentgenograms. A total of 123/142 ulcers, 109 benign, 14 malignant, were available for complete follow-up. Gastroscopy was correct in 106 of 109 benign ulcers visualized. Roentgenoscopy demonstrated 91 of 109, of which 7 were incorrectly called carcinoma. Gross diagnosis was correct by gastroscopy in 11 of 14 malignant ulcers. Radiology visualized 6 of 14; gross diagnosis was correct in 1 of 6 (5 called benign). Directed gastroscopic biopsy was negative for malignant changes in all 109 benign and 3 of 14 malignant ulcers. Total complete gastroscopic diagnostic failures were 4 of 123, for an overall accuracy of 96.7%. Overall roentgenographic accuracy was 70.8%.