We describe a case of a 15-month-old female child admitted to our hospital because of fever, rash, neurological signs (oscillation between states of irritability and drowsiness), palpebral edema and drooping eyelid, appeared 10 days after the vaccination for measles, mumps and rubella. Brain MRI images showed multiple bilateral hyperintense lesions in the white matter typical of acute disseminated encephalomyelitis (ADEM), an autoimmune demyelinating disorder with inflammatory lesions of the central nervous system, due to viral antigens or vaccines. In the mean time, because of patient's vague phenotypic manifestations, suggestive of a genetic defect, array comparative genomic hybridization was carried out which showed the presence of a microdeletion 22q11.21, linked to the DiGeorge syndrome. Our case suggests that pediatric cases of post-vaccination ADEM, in which neurological signs persist, should be investigated for genetic phenotypical features, in order to exclude the presence of a genetic syndrome or disease.