AIM:To examine the demographic data on a large multi-ethnic population of patients with microscopic colitis (MC) in Southern California and to determine the association of MC with inflammatory bowel disease (IBD) and colorectal cancer.METHODS: All patients diagnosed with MC by colonic biopsy from 1996-2005 were identified utilizing a pathology database. All biopsies were reviewed by experienced pathologists utilizing standard histologic criteria. Patients’ medical records were reviewed and data regarding patient age, co-morbidities, sex, ethnicity, and medications were analyzed. An age-and sexmatched standard control group was also generated. Chi-square test was used to evaluate the associations of co-morbidities between lymphocytic colitis (LC), collagenous colitis (CC) and the control group.RESULTS: A total of 547 cases of MC were identif ied,376 patients with LC and 171 patients with CC. The female/male ratio was 3:1 in CC and 2.7:1 in LC patients. Celiac disease (P<0.001), irritable bowel syndrome (IBS) (P<0.001), and thyroid diseases (P<0.001) were found to have a higher occurrence in MC compared to the control group. No statistical differences in the occurrence of colorectal cancer, diabetes and IBD were found between the MC group and the control group.CONCLUSION: This is the largest group of patients with MC known to the authors that has been studied to date. Conditions such as celiac disease, IBS, and thyroid diseases were found to be related to MC. Furthermore, neither an increased risk of colorectal cancer nor IBD was associated with MC in this study. AIM: To examine the demographic data on a large multi-ethnic population of patients with microscopic colitis (MC) in Southern California and determine the association of MC with inflammatory bowel disease (IBD) and colorectal cancer. METHODS: All patients diagnosed with MC All biopsies were reviewed by experienced pathologists utilizing standard histologic criteria. Patients’ medical records were reviewed and data regarding patient age, co-morbidities, sex, ethnicity, and medications analyzed . An age-and sexmatched standard control group was also generated. Chi-square test was used to evaluate the associations of co-morbidities between lymphocytic colitis (LC), collagenous colitis (CC) and the control group .RESULTS: A total of 547 The cases of MC were identified, 376 patients with LC and 171 patients with CC. The female / male ratio was 3: 1 in CC and 2.7: 1 in LC patients. Celiac disease (P <0.001), irritabl No statistical differences in the occurrence of colorectal cancer, diabetes and IBD were found (P <0.001), and thyroid diseases (P <0.001) were found to have a higher occurrence in MC compared to the control group between the MC group and the control group. CONCLUSION: This is the largest group of patients with MC known to the authors that has been studied to date. Conditions such as celiac disease, IBS, and thyroid diseases were found to be related to MC. Furthermore, neither an increased risk of colorectal cancer nor IBD was associated with MC in this study.