To date, there is no available epidemiological study about prognostic factors of acute disseminated encephalomyelitis (ADEM) in children, using a cohort of patients with homogenous inclusion criteria. We aimed to evaluate prognostic factors for relapse after ADEM in children. A total of 132 children from the French National KIDSEP Neuropediatric Cohort (mean age at onset: 6+/-3.3 years; mean follow-up: 5.4+/-3.3 years; lost to follow-up: 10%). ADEM diagnosis was considered in a previously healthy patient acutely presenting more than one neurological deficit, change in mental state and MRI alterations including white matter changes. We used multivariate survival analysis (Cox model) evaluating the prognostic value of baseline clinical, biological and MRI covariates, for the occurrence of a second attack. Twenty-four (18%) of included patients had a second attack. An increased risk of relapse was associated with optic neuritis (hazard ratio, 5.23; 95% CI, 2-13.65), familial history of central nervous system inflammatory demyelination (7.79; 1.54-39.5), Barkhof multiple sclerosis (MS) criteria on MRI (2.52; 1.04-6.12) and no neurological sequelae after first attack (3.79; 1.12-12.85). Clinical and MRI prognostic factors for relapse in ADEM may contribute to an early distinction between monophasic and relapsing disease, which may be related to MS.