Objective To assess the association between diet quality and intake of specific foods with disability and symptom severity in people with multiple sclerosis (MS). Methods In 2015, participants in the North American Research Committee on MS (NARCOMS) Registry completed a dietary screener questionnaire that estimates intake of fruits, vegetables and legumes, whole grains, added sugars, and red/processed meats. We constructed an overall diet quality score for each individual based on these food groups; higher scores denoted a healthier diet. We assessed the association between diet quality and disability status as measured using Patient-Determined Disease Steps (PDDS) and symptom severity using proportional odds models, adjusting for age, sex, income, body mass index, smoking status, and disease duration. We assessed whether a composite healthy lifestyle measure, a healthier diet, healthy weight (body mass index <25), routine physical activity, and abstinence from smoking was associated with symptom severity. Results Of the 7,639 (68%) responders, 6,989 reported physician-diagnosed MS and provided dietary information. Participants with diet quality scores in the highest quintile had lower levels of disability (PDDS; proportional odds ratio [OR] for Q5 vs Q1 0.80; 95% confidence interval [CI] 0.69-0.93) and lower depression scores (proportional OR for Q5 vs Q1 0.82; 95% CI 0.70-0.97). Individuals reporting a composite healthy lifestyle had lower odds of reporting severe fatigue (0.69; 95% CI 0.59-0.81), depression (0.53; 95% CI 0.43-0.66), pain (0.56; 95% CI 0.48-0.67), or cognitive impairment (0.67; 95% CI 0.55-0.79). Conclusions Our large cross-sectional survey suggests a healthy diet and a composite healthy lifestyle are associated with lesser disability and symptom burden in MS.