A 58-year-old woman with severe constipation and a habit of straining at defecation was diagnosed to have mucosal prolapse syndrome. One year later, her primary symptom changed to bloody diarrhea. The colonoscopic and histological findings were consistent with the characteristics of cap polyposis. After nine years, her symptoms and colonoscopic abnormalities disappeared completely without treatment. For two years since that time, the patient has remained well with normal endoscopy findings and a high value of anti-Helicobacter pylori immunoglobulin G. In this case, cap polyposis might have developed via mucosal prolapse syndrome and then regressed completely, irrespective of the Helicobacter pylori infection.