Background/aim: Irritable bowel syndrome (IBS) is a gastrointestinal condition characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any organic cause. This trial investigated the presence of microscopic colitis (MC) and associated factors related to MC in patients diagnosed with IBS. Materials and methods: The study group (group I) consisted of 91 consecutive patients diagnosed with IBS based on the Rome III Criteria for whom colonoscopic examination was requested. The control group (group II) had 41 patients diagnosed with IBS considered as eligible for colonoscopic investigation due to specific conditions, and for whom colonoscopic examination was recommended for screening purposes due to a familial history of colon cancer. Clinical data, endoscopic findings, and the effects of the therapy were evaluated. Results: In the diarrhea-predominant IBS group, nine patients (9.89%) were diagnosed with microscopic colitis, seven with lymphocytic colitis (7.69%), and two with collagenous colitis (CC) (2.19%). None of the patients in group II were found to have MC (P = 0.007). There were no diagnoses of MC in the constipation-predominant and mixed type IBS groups. Conclusion: Clinicians should keep MC in mind for patients presenting with diarrhea-predominant IBS symptoms.