Multiple Sclerosis (MS) is rare in children. Little research exists regarding emotional and behavioral disorders in childhood-onset MS, despite the occurrence of such problems in adults with MS. This paper describes the cognitive and behavioral characteristics of a boy diagnosed with MS at age 9 and mood disorder at age 10. He displayed no cognitive or behavioral problems prior to the onset of physical symptoms of MS. Three years after diagnosis, this child showed persistent problems with speed of processing, visual-motor skills, and parent and teacher-reported executive functioning. In addition, he had difficulties with emotional lability, behavioral disinhibition, depression, and social interaction. As with adults, children with MS may be at increased risk for mood disorder compared to their peers. Mood disorders in children with MS are likely to be multiply determined, although the specific causal mechanisms are unknown.