Background/Objectives: The role of Helicobacter pylori in the pathogenesis of irritable bowel syndrome (IBS) was investigated in 38 subjects, including 16 males (42%) and 22 females (58%), all of who had been diagnosed with IBS but showed no improvement in response to treatment. Methods: Colonoscopy, biopsy and rapid urease test (CLO-test). Results: Nineteen patients were H. pylori-positive (50%) and 19 were H. pylori-negative (50%). One patient in this study previously presented colonic carcinoma. Conclusions: All H. pylori-positive patients received treatment and showed improvement, including the patient with colonic carcinoma. Initially, the carcinoma presented 99% of stenosis, but after one month of treatment the stenosis had decreased to 50%. As a result of this investigation, we consider that the presence of H. pylori in the colonic mucosa is another important co-factor in the pathogenesis of IBS that should also be considered in the development of colonic carcinoma.