An unselected outpatient population of 280 individuals with multiple sclerosis was surveyed to determine the prevalence of bowel dysfunction and to define their characteristics and their relationship to the nongastrointestinal manifestations of the disease. Constipation was present in 43%, was similar in frequency in both sexes, and was more common in patients, regardless of degree of disability, than in a control population. Frequency of constipation also correlated with duration of disease and genitourinary symptoms but did not correlate with use of any medications in mildly disabled patients. Fecal incontinence had occurred at least once in the preceding 3 mo in 51% of patients and once per week or more frequently in 25% of patients who were questioned in more detail with a follow-up questionnaire. Correlations of fecal incontinence with disability, duration of disease, and presence of genitourinary symptoms were similar to constipation. The prevalence of bowel dysfunction (constipation and/or fecal incontinence) in the multiple sclerosis population was 68%, and this manifestation was common even in mildly disabled subjects. Bowel dysfunction can be a source of considerable ongoing social disability in patients with multiple sclerosis. Further studies are needed to characterize the pathophysiology of this common disorder so that effective therapeutic strategies can be identified.