There is a paucity of literature on the epidemiology of severe acute disseminated encephalomyelitis (ADEM). We describe a Paediatric Intensive Care Unit (PICU) population-based study to determine the epidemiology and clinical characteristics of children with ADEM requiring PICU admission or resulting in death. Anonymized data from the Paediatric Intensive Care Audit Network (PICANet) were obtained for all children under 16 years with a diagnosis of ADEM admitted to 25 PICUs in England and Wales (2004-2008). The Office for National Statistics (ONS) mortality database was also searched. In total, 27 PICANet cases (13 females:14 males; median age 4.8 years) were ascertained and all were alive on discharge. In addition, three cases were identified from the ONS mortality database. Of the 27 PICANet cases, clinical features included; seizures (n = 5); upper airway respiratory obstruction/stridor (n = 2); unspecified encephalopathy (n = 27); and polyfocal neurological deficits (n = 6). The median duration of ventilation was 3 days. Inotropic support was required in 4/27 patients, and one patient had invasive intracranial pressure monitoring. None received plasmapheresis. We conclude that the incidence of childhood ADEM admitted to the PICU in England and Wales is approximated at 0.5 per million children/year, thus representing approximately one quarter of children admitted with ADEM (denominator: 2009 Canadian surveillance data).