Microscopic Colitis (MC) and diarrhea predominant irritable bowel syndrome (IBS-D) has almost similar clinical feature but MC is diagnosed by histologic criteria and IBS is diagnosed by symptom based criteria. There is ongoing debate about the importance of biopsies from endoscopically normal colonic mucosa in the investigation of patients with IBS-D. Aim of this study was to assess the prevalence of MC in patient with IBS-D and to determine the distribution of MC in the colon. This observational study was conducted in department of Gastroenterology, Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka, Bangladesh from January 2008 to December 2009. Patients were evaluated thoroughly & who meet Rome–II criteria with normal routine laboratory tests, were included in the study.