Background: Although profound hypochlorhydria is considered to be an important risk factor for development of gastric cancer, long-term effect of Helicobacter pylori eradication on its reversibility remains uncertain. Aim: To clarify the change in acid secretion after eradication in a long-term follow-up over 5 years in patients with profound hypochlorhydria. Methods: Twenty-three H. pylori-positive patients with hypochlorhydria (<0.6 mmol/10 min) were enrolled prospectively. Assessment of gastrin-stimulated acid output and histologic evaluation of biopsy specimens were performed prior to, and 1, 7 months after eradication. Subsequently, gastric acid secretion was assessed for long-term period over 5 years after eradication in 12 patients. Results: Gastric acid secretion was reversed to normal range in nine of 23 patients (39%) at 7 months after eradication. In the long-term follow-up, gradual and significant recovery in gastric acid secretion was observed up to 2 years post-therapy. However, there was no additional increase during the last 3 years of 5-year follow-up period, leaving the acid secretory levels subnormal in the majority of the patients. Conclusions: This long-term follow-up study suggests that the pathologic process has already progressed to an irreversible stage in the majority of H. pylori-positive patients with marked body atrophy and profound hypochlorhydria.