A 32-year-old man presented to the internal medicine clinic with a 2-week history of epigastric pain, nausea, anorexia, and weight loss. Physical examination was notable for epigastric tenderness. A computed tomographic scan of the abdomen showed mural thickening of the gastric antrum. Endoscopy revealed an ulcer measuring 4.0 cm by 5.0 cm in the gastric antrum (Panel A) and an ulcer measuring 1.2 cm by 1.2 cm on the greater antral curvature (Panel B). Biopsy samples of the ulcers showed infiltration of lymphocytes, neutrophils, and plasma cells. There were no malignant features. Further history taking revealed that the patient had had a genital ulcer 1 month before presentation. A subsequent serum Treponema pallidum particle agglutination test was positive, and the rapid plasma reagin (RPR) titer was 1:128. Immunohistochemical staining of the ulcer-biopsy specimens for T. pallidum was positive (Panel C). Testing for the human immunodeficiency virus was negative. A diagnosis of gastric syphilis was made. Once-weekly injections of penicillin G benzathine were given for 3 weeks. Two weeks after the patient began treatment, his symptoms had abated. Four months after the completion of treatment, repeat testing showed that the RPR titer had decreased to 1:4, and a repeat endoscopy showed that the ulcers had resolved (Panel D, arrows).