Chronic atrophic gastritis and a sessile polyp were diagnosed during gastroscopy of a patient with splenomegaly and portal hypertension. The polyp was removed endoscopically. Histologically, it proved to be an endocrine tumour, which was identified as gastrinoma by immunohistochemistry. Then, hypergastrinemia was found and gastrectomy was performed to ensure complete removal of the tumour. The surgical specimen showed G cell hyperplasia of the antro-pyloric mucosa and severe atrophic gastritis with scattered argyrophil micronodules in the corpus-fundus region. 3 years after this treatment the patient is well.