We describe seven patients with Helicobacter pylori acute gastritis who presented endoscopical picture simulating gastric carcinoma or lymphoma. H. pylori was detected on the antral and on the oxyntic mucosa of all patients. At histological examination, no evidence of malignancy was observed in any of the patients. In the antral mucosa there were edema, hyperemia, and intense polymorphonuclear leukocyte infiltration (neutrophils and some eosinophils) in the lamina propria, mucus layer, and inside the glands. The patients were treated with amoxycillin (2 g/day for 2 months) associated with metronidazole (750 mg/day for 15 days), which reduced the symptoms dramatically. Endoscopy and biopsy, repeated 4 wk after treatment was stopped, showed that the patients had been cleared of H. pylori, and indicated a marked improvement of endoscopical and histological gastritis. These findings indicated that H. pylori acute gastritis can mimic gastric carcinoma or lymphoma. Therefore, histology and detection of H. pylori are essential for an accurate diagnosis.