BACKGROUND It is controversial as to whether the development of gastric cancer is influenced by Helicobacter pylori eradication. If eradication itself influences the tumour morphology, this may affect the tumour discovery rate. OBJECTIVE To investigate the morphological changes in the gastric neoplasm after H. pylori eradication. METHODS We studied 37 patients with eradication therapy. After a 1-month follow-up, endoscopic re-evaluation was performed and the appearance was compared with first image. All lesions were resected endoscopically, and were subjected to histological assessment and to immunohistochemistry. Serum gastrin levels were determined before and after eradication. RESULTS Twenty-nine of 37 patients underwent successful eradication. The appearance of 11 lesions (33% of 33 lesions) became indistinct after successful eradication. All lesions were of the superficial-elevated type and the height of the lesions decreased. We detected normal columnar epithelium over the neoplasm in eight of the lesions. Higher expression of single-stranded deoxyribonucleic acid in the deep area was characteristic in tumours with an indistinct appearance. These changes did not correlate with the serum gastrin levels. CONCLUSIONS The morphology of the gastric neoplasm change after eradication in the short-term. This may contribute to the decreased tumour discovery rate.