BACKGROUND: Multiple sclerosis (MS) and allergies are both considered to be related to imbalanced Th1 and Th2 immune responses. Previous studies evaluating the relationship between MS and allergies provide conflicting results. OBJECTIVE: To assess allergies and asthma as risk factors for MS and as predictors of MS relapses in a pediatric cohort. METHODS: The environment and genetic risk factors for pediatric MS study is a national case-control project with 16 participating US sites. An environmental questionnaire is used that includes history of allergies in the first five years of life. Case-control data are entered in the pediatric MS Network database and cases at 12 of the 16 sites enter relapse data prospectively. Annualized relapse rate was calculated for patients with follow-up and adjusted for age at disease onset, gender, race, ethnicity, and use of disease-modifying therapy (DMT). RESULTS: We included 271 cases (mean age at disease onset of 15.7years and 62% female) and 418 controls. Relapse data were available for 193 cases. There was no difference in prevalence of allergies or asthma between cases and controls. Patients with food allergies had fewer relapses compared to patients without food allergies (0.14 vs 0.48, p=0.01). CONCLUSIONS: While allergies and asthma are not associated with pediatric MS, cases with food allergies have fewer relapses compared to those without food allergies.