We conducted a study on 152 patients with multiple sclerosis (MS) who were born in North Africa and migrated to France. Information was obtained from patients on common childhood infections. We found that, in most cases, common childhood illnesses occurred before migration, but these infections occurred at later ages when the patients were in France: the mean differences were equal to 3 years for measles, 2.1 years for chickenpox, and 4.5 years for mumps. In comparison with data available for the general populations of Algeria and France, the mean ages of childhood infections, and particularly measles, were higher in MS patients. Data confirm that, wherever they live, MS patients tend to have childhood infections at a relatively late age and suggest that migration delays the age of viral infections. This might be one of the possible explanations for the effect of migration on the risk of MS.