Gliomatosis cerebri (GC) is a diffuse infiltrating glial neoplasm of astrocytic origin. GC in children is rare and difficult to diagnose, often presenting with a variety of signs and symptoms that may mimic encephalitis. We discuss here the presentation and diagnosis of GC in 2 children who were initially suspected to have acute disseminating encephalomyelitis. In this report we underscore the limitations of relying on clinical presentation and neuroimaging as well as the essential role of pathologic evaluation for the diagnosis of GC in children.