OBJECTIVES: To quantify the coexistence of inflammatory bowel disease (IBD) and multiple sclerosis (MS) and to characterize the diseases when they coexist. PATIENTS AND METHODS: In this retrospective study of medical records spanning 1950 through 1995, the diagnoses of Crohn disease (CD), ulcerative colitis (UC), and MS were based on review of inpatient and outpatient records by a gastroenterologist and a neurologist. RESULTS: We identified 4 residents of Olmsted County, Minnesota, with IBD (3 UC, 1 CD) who had concurrent, clinically definite MS; all had mild neurologic disease with little disability. These comprised 1% of the IBD and 1.8% of the MS cohort. The CD patient had undergone terminal ileal resection; of the UC patients, 2 had pancolitis, and 1 had proctosigmoiditis. The observed prevalence of MS at onset of IBD was 3.7 times the expected (95% confidence interval, 0.8-10.8). We also reviewed the records of 32 referral patients with both diagnoses. Disability from MS was moderate at median follow-up of 8.5 years. By 15 years, ambulation was impaired in most patients. Neurologic disability was similar between patients with CD and UC. CONCLUSIONS: Concurrence of the 2 diseases was greater than expected. Although MS and IBD may share common predisposing factors, not enough information is available to speculate about possible mechanisms.