Gastric involvement in secondary or tertiary syphilis is rarely recognized clinically, and its diagnosis by examination of endoscopic biopsy specimens has been reported infrequently. We report four cases of gastric syphilis with the primary diagnosis made by gastric biopsy. The patients, all male, ranged in age from 38 to 78 years and presented with gastric complaints, the most common being upper gastrointestinal tract bleeding (three of four). Gastroscopy showed either erosive gastritis or gastric ulcers with heaped, nodular edges. The clinical diagnoses ranged from benign ulcer disease to infiltrating carcinoma and lymphoma. Gastric biopsy specimens in all cases showed a severe gastritis with dense plasmacytic infiltration, associated with varying numbers of polymorphonuclear leukocytes and lymphocytes, variable degrees of glandular destruction and reactive atypia, and a vasculitis without proliferative changes. Modified Steiner silver impregnation stain revealed numerous spirochetes in all four cases and associated Helicobacter pylori infection in one case. Serologic studies for syphilis were positive in all four cases (rapid plasma reagin test, fluorescent treponemal antibody absorption test). None of the patients were seroreactive for antibodies to human immunodeficiency virus. These recent cases of gastric syphilis emphasize the importance of remaining alert to the protean clinical manifestations of syphilis and aware of the histopathologic patterns of this disease.