The initial presenting clinical and laboratory findings of either acute disseminated encephalomyelitis or the first attack of multiple sclerosis in the pediatric population were compared and contrasted. A retrospective review of the medical records was conducted of all children younger than 17 years who presented with either the diagnosis of acute disseminated encephalomyelitis or multiple sclerosis between 1987 and 2001. Seventeen cases of clinically definite multiple sclerosis (seven female, mean age 12.4 +/- 4.5 years) and seven cases of acute disseminated encephalomyelitis (three female; mean age 8.7 +/- 3.8 years) were reviewed. Systemic and nonfocal neurologic symptoms were more commonly evident in acute disseminated encephalomyelitis than in multiple sclerosis fever (43% vs 6%), headache (57% vs 24%), fatigue (71% vs 29%), vomiting (57% vs 0%), and encephalopathy (71% vs 6%). In multiple sclerosis patients, T(2)-weighted white matter magnetic resonance imaging lesions were more commonly located in the corpus callosum (64% vs 17%) and the periventricular area (91% vs 50%) compared with those in patients with acute disseminated encephalomyelitis. These results suggest that acute disseminated encephalomyelitis and multiple sclerosis can be differentiated to some degree according to clinical and radiologic data at initial presentation, which is important because the long-term prognosis for childhood multiple sclerosis appears to be less favorable.