In our previous study, we found the presence of serum autoantibody against arrestin in patients with multiple sclerosis (MS), while such serum autoantibody was not detected from patients with other neurological diseases and control subjects. We suggested that serum arrestin antibody titers may be useful for the diagnosis and evaluation of the disease's course. In the present study we examined sera from 7 patients, who were initially diagnosed as having acute disseminated encephalomyelitis (ADEM), for the presence of serum antibody against arrestin, in order to study the specificity of the serum antibody among demyelinated diseases. High titers were detected from 2 patients out of 7. One of the patients, a 4 year-old girl, presented with an additional neurological attack during the 6 months after the initial attack, resulting in change of diagnosis to MS. During her disease course the serum titers against arrestin fluctuated in correspondence with the disease's activity. These observations suggest that the presence of serum autoantibody against arrestin may be specific to MS and be helpful for differential diagnosis of ADEM and MS.