Obesity is one possible contributor to severity of multiple sclerosis and progression of the disease. We already know that obesity is a risk determinant for acquiring MS, yet the impact of obesity on pediatric MS disease expression and course is unknown. This study will evaluate the relationship between obesity, obesity-derived inflammatory mediators, and imaging metrics of MS severity in children. Understanding how childhood obesity contributes to MS severity/progression may yield fundamental insights into disease pathobiology - which may thereby lead to effective strategies for halting its progression in its earliest stages.