This study explored the prevalence of comorbid conditions in hospitalized patients with multiple sclerosis (MS) who were 65 years of age or older. Using 1989 data from the Quality of Care Medicare Provider Analysis and Review (MEDPAR) file, hospitalized MS patients were compared with respect to discharge diagnoses to an age- and sex-matched group of hospitalized patients without MS. As expected, the following discharge diagnoses were more common (P < 0.05) for MS patients: urinary tract infection, pneumonia, septicemia and cellulitus. In contrast, MS patients were less likely (P < 0.05) to have discharge diagnoses of acute myocardial infarction, heart failure, hypertension, angina pectoris, cerebrovascular disease, diabetes mellitus and chronic obstructive pulmonary disease. Possible explanations include under-reporting of certain comorbid conditions on discharge records of MS patients, a protective effect of MS or its treatment, reduced prevalence of risk factors, disproportionate mortality in younger MS patients with comorbidity and the benefits of medical surveillance.