Acute, acquired demyelination of central nervous system in childhood leads to a variety of clinical phenotypes dependant on the site of demyelination and presence of encephalopathy. Posterior fossa involvement is seen in over third of cases in childhood. We report on four children who had cerebellar involvement with significant mass effect in posterior fossa on CT and MRI brain. This subgroup of children have significant cerebellar and brainstem swelling (rhombencephalitis) and is difficult to distinguish entirely on clinical grounds from other children with acute demyelinating events at presentation.